extract a couple of files

4 files changed, 1202 insertions, 1193 deletions

diff --git a/search.lua b/search.lua
new file mode 100644
index 0000000..29dd8dd
--- /dev/null
+++ b/search.lua
@@ -0,0 +1,114 @@
+-- helpers for the search bar (C-f)
+
+function Text.draw_search_bar()
+  local h = Line_height+2
+  local y = App.screen.height-h
+  love.graphics.setColor(0.9,0.9,0.9)
+  love.graphics.rectangle('fill', 0, y-10, App.screen.width-1, h+8)
+  love.graphics.setColor(0.6,0.6,0.6)
+  love.graphics.line(0, y-10, App.screen.width-1, y-10)
+  love.graphics.setColor(1,1,1)
+  love.graphics.rectangle('fill', 20, y-6, App.screen.width-40, h+2, 2,2)
+  love.graphics.setColor(0.6,0.6,0.6)
+  love.graphics.rectangle('line', 20, y-6, App.screen.width-40, h+2, 2,2)
+  love.graphics.setColor(0,0,0)
+  App.screen.print(Search_term, 25,y-5)
+  love.graphics.setColor(1,0,0)
+  if Search_text == nil then
+    Search_text = App.newText(love.graphics.getFont(), Search_term)
+  end
+  love.graphics.circle('fill', 25+App.width(Search_text),y-5+h, 2)
+  love.graphics.setColor(0,0,0)
+end
+
+function Text.search_next()
+  -- search current line
+  local pos = Lines[Cursor1.line].data:find(Search_term, Cursor1.pos)
+  if pos then
+    Cursor1.pos = pos
+  end
+  if pos == nil then
+    for i=Cursor1.line+1,#Lines do
+      pos = Lines[i].data:find(Search_term)
+      if pos then
+        Cursor1.line = i
+        Cursor1.pos = pos
+        break
+      end
+    end
+  end
+  if pos == nil then
+    -- wrap around
+    for i=1,Cursor1.line-1 do
+      pos = Lines[i].data:find(Search_term)
+      if pos then
+        Cursor1.line = i
+        Cursor1.pos = pos
+        break
+      end
+    end
+  end
+  if pos == nil then
+    Cursor1.line = Search_backup.cursor.line
+    Cursor1.pos = Search_backup.cursor.pos
+    Screen_top1.line = Search_backup.screen_top.line
+    Screen_top1.pos = Search_backup.screen_top.pos
+  end
+  if Text.lt1(Cursor1, Screen_top1) or Text.lt1(Screen_bottom1, Cursor1) then
+    Screen_top1.line = Cursor1.line
+    local _, pos = Text.pos_at_start_of_cursor_screen_line()
+    Screen_top1.pos = pos
+  end
+end
+
+function Text.search_previous()
+  -- search current line
+  local pos = rfind(Lines[Cursor1.line].data, Search_term, Cursor1.pos)
+  if pos then
+    Cursor1.pos = pos
+  end
+  if pos == nil then
+    for i=Cursor1.line-1,1,-1 do
+      pos = rfind(Lines[i].data, Search_term)
+      if pos then
+        Cursor1.line = i
+        Cursor1.pos = pos
+        break
+      end
+    end
+  end
+  if pos == nil then
+    -- wrap around
+    for i=#Lines,Cursor1.line+1,-1 do
+      pos = rfind(Lines[i].data, Search_term)
+      if pos then
+        Cursor1.line = i
+        Cursor1.pos = pos
+        break
+      end
+    end
+  end
+  if pos == nil then
+    Cursor1.line = Search_backup.cursor.line
+    Cursor1.pos = Search_backup.cursor.pos
+    Screen_top1.line = Search_backup.screen_top.line
+    Screen_top1.pos = Search_backup.screen_top.pos
+  end
+  if Text.lt1(Cursor1, Screen_top1) or Text.lt1(Screen_bottom1, Cursor1) then
+    Screen_top1.line = Cursor1.line
+    local _, pos = Text.pos_at_start_of_cursor_screen_line()
+    Screen_top1.pos = pos
+  end
+end
+
+function rfind(s, pat, i)
+  local rs = s:reverse()
+  local rpat = pat:reverse()
+  if i == nil then i = #s end
+  local ri = #s - i + 1
+  local rendpos = rs:find(rpat, ri)
+  if rendpos == nil then return nil end
+  local endpos = #s - rendpos + 1
+  assert (endpos >= #pat)
+  return endpos-#pat+1
+end
diff --git a/select.lua b/select.lua
new file mode 100644
index 0000000..fcef878
--- /dev/null
+++ b/select.lua
@@ -0,0 +1,153 @@
+-- helpers for selecting portions of text
+
+local utf8 = require 'utf8'
+
+-- Return any intersection of the region from Selection1 to Cursor1 (or
+-- current mouse, if mouse is pressed; or recent mouse if mouse is pressed and
+-- currently over a drawing) with the region between {line=line_index, pos=apos}
+-- and {line=line_index, pos=bpos}.
+-- apos must be less than bpos. However Selection1 and Cursor1 can be in any order.
+-- Result: positions spos,epos between apos,bpos.
+function Text.clip_selection(line_index, apos, bpos)
+  if Selection1.line == nil then return nil,nil end
+  -- min,max = sorted(Selection1,Cursor1)
+  local minl,minp = Selection1.line,Selection1.pos
+  local maxl,maxp
+  if love.mouse.isDown('1') then
+    maxl,maxp = Text.mouse_pos()
+  else
+    maxl,maxp = Cursor1.line,Cursor1.pos
+  end
+  if minl > maxl then
+    minl,maxl = maxl,minl
+    minp,maxp = maxp,minp
+  elseif minl == maxl then
+    if minp > maxp then
+      minp,maxp = maxp,minp
+    end
+  end
+  -- check if intervals are disjoint
+  if line_index < minl then return nil,nil end
+  if line_index > maxl then return nil,nil end
+  if line_index == minl and bpos <= minp then return nil,nil end
+  if line_index == maxl and apos >= maxp then return nil,nil end
+  -- compare bounds more carefully (start inclusive, end exclusive)
+  local a_ge = Text.le1({line=minl, pos=minp}, {line=line_index, pos=apos})
+  local b_lt = Text.lt1({line=line_index, pos=bpos}, {line=maxl, pos=maxp})
+--?   print(minl,line_index,maxl, '--', minp,apos,bpos,maxp, '--', a_ge,b_lt)
+  if a_ge and b_lt then
+    -- fully contained
+    return apos,bpos
+  elseif a_ge then
+    assert(maxl == line_index)
+    return apos,maxp
+  elseif b_lt then
+    assert(minl == line_index)
+    return minp,bpos
+  else
+    assert(minl == maxl and minl == line_index)
+    return minp,maxp
+  end
+end
+
+-- inefficient for some reason, so don't do it on every frame
+function Text.mouse_pos()
+  local time = love.timer.getTime()
+  if Recent_mouse.time and Recent_mouse.time > time-0.1 then
+    return Recent_mouse.line, Recent_mouse.pos
+  end
+  Recent_mouse.time = time
+  local line,pos = Text.to_pos(love.mouse.getX(), love.mouse.getY())
+  if line then
+    Recent_mouse.line = line
+    Recent_mouse.pos = pos
+  end
+  return Recent_mouse.line, Recent_mouse.pos
+end
+
+function Text.to_pos(x,y)
+  for line_index,line in ipairs(Lines) do
+    if line.mode == 'text' then
+      if Text.in_line(line, x,y) then
+        return line_index, Text.to_pos_on_line(line, x,y)
+      end
+    end
+  end
+end
+
+function Text.delete_selection()
+  local minl,maxl = minmax(Selection1.line, Cursor1.line)
+  local before = snapshot(minl, maxl)
+  Text.delete_selection_without_undo()
+  record_undo_event({before=before, after=snapshot(Cursor1.line)})
+end
+
+function Text.delete_selection_without_undo()
+  if Selection1.line == nil then return end
+  -- min,max = sorted(Selection1,Cursor1)
+  local minl,minp = Selection1.line,Selection1.pos
+  local maxl,maxp = Cursor1.line,Cursor1.pos
+  if minl > maxl then
+    minl,maxl = maxl,minl
+    minp,maxp = maxp,minp
+  elseif minl == maxl then
+    if minp > maxp then
+      minp,maxp = maxp,minp
+    end
+  end
+  -- update Cursor1 and Selection1
+  Cursor1.line = minl
+  Cursor1.pos = minp
+  Selection1 = {}
+  -- delete everything between min (inclusive) and max (exclusive)
+  Lines[minl].fragments = nil
+  Lines[minl].screen_line_starting_pos = nil
+  local min_offset = utf8.offset(Lines[minl].data, minp)
+  local max_offset = utf8.offset(Lines[maxl].data, maxp)
+  if minl == maxl then
+--?     print('minl == maxl')
+    Lines[minl].data = Lines[minl].data:sub(1, min_offset-1)..Lines[minl].data:sub(max_offset)
+    return
+  end
+  assert(minl < maxl)
+  local rhs = Lines[maxl].data:sub(max_offset)
+  for i=maxl,minl+1,-1 do
+    table.remove(Lines, i)
+  end
+  Lines[minl].data = Lines[minl].data:sub(1, min_offset-1)..rhs
+end
+
+function Text.selection()
+  if Selection1.line == nil then return end
+  -- min,max = sorted(Selection1,Cursor1)
+  local minl,minp = Selection1.line,Selection1.pos
+  local maxl,maxp = Cursor1.line,Cursor1.pos
+  if minl > maxl then
+    minl,maxl = maxl,minl
+    minp,maxp = maxp,minp
+  elseif minl == maxl then
+    if minp > maxp then
+      minp,maxp = maxp,minp
+    end
+  end
+  local min_offset = utf8.offset(Lines[minl].data, minp)
+  local max_offset = utf8.offset(Lines[maxl].data, maxp)
+  if minl == maxl then
+    return Lines[minl].data:sub(min_offset, max_offset-1)
+  end
+  assert(minl < maxl)
+  local result = Lines[minl].data:sub(min_offset)..'\n'
+  for i=minl+1,maxl-1 do
+    if Lines[i].mode == 'text' then
+      result = result..Lines[i].data..'\n'
+    end
+  end
+  result = result..Lines[maxl].data:sub(1, max_offset-1)
+  return result
+end
+
+function Text.cut_selection()
+  local result = Text.selection()
+  Text.delete_selection()
+  return result
+end
diff --git a/text.lua b/text.lua
index 8412cfb..e57a019 100644
--- a/text.lua
+++ b/text.lua
@@ -1,9 +1,12 @@
--- primitives for editing text
+-- text editor, particularly text drawing, horizontal wrap, vertical scrolling
 Text = {}
 
 local utf8 = require 'utf8'
 
+require 'search'
+require 'select'
 require 'undo'
+require 'text_tests'
 
 -- return values:
 --  y coordinate drawn until in px
@@ -104,269 +107,6 @@ end
 -- manual tests:
 --  draw with small line_width of 100
 
-function Text.draw_search_bar()
-  local h = Line_height+2
-  local y = App.screen.height-h
-  love.graphics.setColor(0.9,0.9,0.9)
-  love.graphics.rectangle('fill', 0, y-10, App.screen.width-1, h+8)
-  love.graphics.setColor(0.6,0.6,0.6)
-  love.graphics.line(0, y-10, App.screen.width-1, y-10)
-  love.graphics.setColor(1,1,1)
-  love.graphics.rectangle('fill', 20, y-6, App.screen.width-40, h+2, 2,2)
-  love.graphics.setColor(0.6,0.6,0.6)
-  love.graphics.rectangle('line', 20, y-6, App.screen.width-40, h+2, 2,2)
-  love.graphics.setColor(0,0,0)
-  App.screen.print(Search_term, 25,y-5)
-  love.graphics.setColor(1,0,0)
-  if Search_text == nil then
-    Search_text = App.newText(love.graphics.getFont(), Search_term)
-  end
-  love.graphics.circle('fill', 25+App.width(Search_text),y-5+h, 2)
-  love.graphics.setColor(0,0,0)
-end
-
-function Text.search_next()
-  -- search current line
-  local pos = Lines[Cursor1.line].data:find(Search_term, Cursor1.pos)
-  if pos then
-    Cursor1.pos = pos
-  end
-  if pos == nil then
-    for i=Cursor1.line+1,#Lines do
-      pos = Lines[i].data:find(Search_term)
-      if pos then
-        Cursor1.line = i
-        Cursor1.pos = pos
-        break
-      end
-    end
-  end
-  if pos == nil then
-    -- wrap around
-    for i=1,Cursor1.line-1 do
-      pos = Lines[i].data:find(Search_term)
-      if pos then
-        Cursor1.line = i
-        Cursor1.pos = pos
-        break
-      end
-    end
-  end
-  if pos == nil then
-    Cursor1.line = Search_backup.cursor.line
-    Cursor1.pos = Search_backup.cursor.pos
-    Screen_top1.line = Search_backup.screen_top.line
-    Screen_top1.pos = Search_backup.screen_top.pos
-  end
-  if Text.lt1(Cursor1, Screen_top1) or Text.lt1(Screen_bottom1, Cursor1) then
-    Screen_top1.line = Cursor1.line
-    local _, pos = Text.pos_at_start_of_cursor_screen_line()
-    Screen_top1.pos = pos
-  end
-end
-
-function Text.search_previous()
-  -- search current line
-  local pos = rfind(Lines[Cursor1.line].data, Search_term, Cursor1.pos)
-  if pos then
-    Cursor1.pos = pos
-  end
-  if pos == nil then
-    for i=Cursor1.line-1,1,-1 do
-      pos = rfind(Lines[i].data, Search_term)
-      if pos then
-        Cursor1.line = i
-        Cursor1.pos = pos
-        break
-      end
-    end
-  end
-  if pos == nil then
-    -- wrap around
-    for i=#Lines,Cursor1.line+1,-1 do
-      pos = rfind(Lines[i].data, Search_term)
-      if pos then
-        Cursor1.line = i
-        Cursor1.pos = pos
-        break
-      end
-    end
-  end
-  if pos == nil then
-    Cursor1.line = Search_backup.cursor.line
-    Cursor1.pos = Search_backup.cursor.pos
-    Screen_top1.line = Search_backup.screen_top.line
-    Screen_top1.pos = Search_backup.screen_top.pos
-  end
-  if Text.lt1(Cursor1, Screen_top1) or Text.lt1(Screen_bottom1, Cursor1) then
-    Screen_top1.line = Cursor1.line
-    local _, pos = Text.pos_at_start_of_cursor_screen_line()
-    Screen_top1.pos = pos
-  end
-end
-
-function rfind(s, pat, i)
-  local rs = s:reverse()
-  local rpat = pat:reverse()
-  if i == nil then i = #s end
-  local ri = #s - i + 1
-  local rendpos = rs:find(rpat, ri)
-  if rendpos == nil then return nil end
-  local endpos = #s - rendpos + 1
-  assert (endpos >= #pat)
-  return endpos-#pat+1
-end
-
--- Return any intersection of the region from Selection1 to Cursor1 (or
--- current mouse, if mouse is pressed; or recent mouse if mouse is pressed and
--- currently over a drawing) with the region between {line=line_index, pos=apos}
--- and {line=line_index, pos=bpos}.
--- apos must be less than bpos. However Selection1 and Cursor1 can be in any order.
--- Result: positions spos,epos between apos,bpos.
-function Text.clip_selection(line_index, apos, bpos)
-  if Selection1.line == nil then return nil,nil end
-  -- min,max = sorted(Selection1,Cursor1)
-  local minl,minp = Selection1.line,Selection1.pos
-  local maxl,maxp
-  if love.mouse.isDown('1') then
-    maxl,maxp = Text.mouse_pos()
-  else
-    maxl,maxp = Cursor1.line,Cursor1.pos
-  end
-  if minl > maxl then
-    minl,maxl = maxl,minl
-    minp,maxp = maxp,minp
-  elseif minl == maxl then
-    if minp > maxp then
-      minp,maxp = maxp,minp
-    end
-  end
-  -- check if intervals are disjoint
-  if line_index < minl then return nil,nil end
-  if line_index > maxl then return nil,nil end
-  if line_index == minl and bpos <= minp then return nil,nil end
-  if line_index == maxl and apos >= maxp then return nil,nil end
-  -- compare bounds more carefully (start inclusive, end exclusive)
-  local a_ge = Text.le1({line=minl, pos=minp}, {line=line_index, pos=apos})
-  local b_lt = Text.lt1({line=line_index, pos=bpos}, {line=maxl, pos=maxp})
---?   print(minl,line_index,maxl, '--', minp,apos,bpos,maxp, '--', a_ge,b_lt)
-  if a_ge and b_lt then
-    -- fully contained
-    return apos,bpos
-  elseif a_ge then
-    assert(maxl == line_index)
-    return apos,maxp
-  elseif b_lt then
-    assert(minl == line_index)
-    return minp,bpos
-  else
-    assert(minl == maxl and minl == line_index)
-    return minp,maxp
-  end
-end
-
--- inefficient for some reason, so don't do it on every frame
-function Text.mouse_pos()
-  local time = love.timer.getTime()
-  if Recent_mouse.time and Recent_mouse.time > time-0.1 then
-    return Recent_mouse.line, Recent_mouse.pos
-  end
-  Recent_mouse.time = time
-  local line,pos = Text.to_pos(love.mouse.getX(), love.mouse.getY())
-  if line then
-    Recent_mouse.line = line
-    Recent_mouse.pos = pos
-  end
-  return Recent_mouse.line, Recent_mouse.pos
-end
-
-function Text.to_pos(x,y)
-  for line_index,line in ipairs(Lines) do
-    if line.mode == 'text' then
-      if Text.in_line(line, x,y) then
-        return line_index, Text.to_pos_on_line(line, x,y)
-      end
-    end
-  end
-end
-
-function Text.delete_selection()
-  local minl,maxl = minmax(Selection1.line, Cursor1.line)
-  local before = snapshot(minl, maxl)
-  Text.delete_selection_without_undo()
-  record_undo_event({before=before, after=snapshot(Cursor1.line)})
-end
-
-function Text.delete_selection_without_undo()
-  if Selection1.line == nil then return end
-  -- min,max = sorted(Selection1,Cursor1)
-  local minl,minp = Selection1.line,Selection1.pos
-  local maxl,maxp = Cursor1.line,Cursor1.pos
-  if minl > maxl then
-    minl,maxl = maxl,minl
-    minp,maxp = maxp,minp
-  elseif minl == maxl then
-    if minp > maxp then
-      minp,maxp = maxp,minp
-    end
-  end
-  -- update Cursor1 and Selection1
-  Cursor1.line = minl
-  Cursor1.pos = minp
-  Selection1 = {}
-  -- delete everything between min (inclusive) and max (exclusive)
-  Lines[minl].fragments = nil
-  Lines[minl].screen_line_starting_pos = nil
-  local min_offset = utf8.offset(Lines[minl].data, minp)
-  local max_offset = utf8.offset(Lines[maxl].data, maxp)
-  if minl == maxl then
---?     print('minl == maxl')
-    Lines[minl].data = Lines[minl].data:sub(1, min_offset-1)..Lines[minl].data:sub(max_offset)
-    return
-  end
-  assert(minl < maxl)
-  local rhs = Lines[maxl].data:sub(max_offset)
-  for i=maxl,minl+1,-1 do
-    table.remove(Lines, i)
-  end
-  Lines[minl].data = Lines[minl].data:sub(1, min_offset-1)..rhs
-end
-
-function Text.selection()
-  if Selection1.line == nil then return end
-  -- min,max = sorted(Selection1,Cursor1)
-  local minl,minp = Selection1.line,Selection1.pos
-  local maxl,maxp = Cursor1.line,Cursor1.pos
-  if minl > maxl then
-    minl,maxl = maxl,minl
-    minp,maxp = maxp,minp
-  elseif minl == maxl then
-    if minp > maxp then
-      minp,maxp = maxp,minp
-    end
-  end
-  local min_offset = utf8.offset(Lines[minl].data, minp)
-  local max_offset = utf8.offset(Lines[maxl].data, maxp)
-  if minl == maxl then
-    return Lines[minl].data:sub(min_offset, max_offset-1)
-  end
-  assert(minl < maxl)
-  local result = Lines[minl].data:sub(min_offset)..'\n'
-  for i=minl+1,maxl-1 do
-    if Lines[i].mode == 'text' then
-      result = result..Lines[i].data..'\n'
-    end
-  end
-  result = result..Lines[maxl].data:sub(1, max_offset-1)
-  return result
-end
-
-function Text.cut_selection()
-  local result = Text.selection()
-  Text.delete_selection()
-  return result
-end
-
 function Text.draw_cursor(x, y)
   love.graphics.setColor(1,0,0)
   love.graphics.circle('fill', x,y+Line_height, 2)
@@ -375,935 +115,6 @@ function Text.draw_cursor(x, y)
   Cursor_y = y+Line_height
 end
 
-function test_draw_text()
-  io.write('\ntest_draw_text')
-  App.screen.init{width=120, height=60}
-  Lines = load_array{'abc', 'def', 'ghi'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_draw_text/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_draw_text/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_draw_text/screen:3')
-end
-
-function test_draw_wrapping_text()
-  io.write('\ntest_draw_wrapping_text')
-  App.screen.init{width=50, height=60}
-  Lines = load_array{'abc', 'defgh', 'xyz'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_draw_wrapping_text/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_draw_wrapping_text/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'gh', 'F - test_draw_wrapping_text/screen:3')
-end
-
-function test_draw_word_wrapping_text()
-  io.write('\ntest_draw_word_wrapping_text')
-  App.screen.init{width=60, height=60}
-  Lines = load_array{'abc def ghi', 'jkl'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc ', 'F - test_draw_word_wrapping_text/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def ', 'F - test_draw_word_wrapping_text/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_draw_word_wrapping_text/screen:3')
-end
-
-function test_draw_text_wrapping_within_word()
-  -- arrange a screen line that needs to be split within a word
-  io.write('\ntest_draw_text_wrapping_within_word')
-  App.screen.init{width=60, height=60}
-  Lines = load_array{'abcd e fghijk', 'xyz'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abcd ', 'F - test_draw_text_wrapping_within_word/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'e fghi', 'F - test_draw_text_wrapping_within_word/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'jk', 'F - test_draw_text_wrapping_within_word/screen:3')
-end
-
-function test_edit_wrapping_text()
-  io.write('\ntest_edit_wrapping_text')
-  App.screen.init{width=50, height=60}
-  Lines = load_array{'abc', 'def', 'xyz'}
-  Line_width = App.screen.width
-  Cursor1 = {line=2, pos=4}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.run_after_textinput('g')
-  App.run_after_textinput('h')
-  App.run_after_textinput('i')
-  App.run_after_textinput('j')
-  App.run_after_textinput('k')
-  App.run_after_textinput('l')
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_edit_wrapping_text/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_edit_wrapping_text/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghij', 'F - test_edit_wrapping_text/screen:3')
-end
-
-function test_insert_newline()
-  io.write('\ntest_insert_newline')
-  -- display a few lines with cursor on bottom line
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=2}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_insert_newline/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_insert_newline/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_insert_newline/baseline/screen:3')
-  -- after hitting the enter key the screen scrolls down
-  App.run_after_keychord('return')
-  check_eq(Screen_top1.line, 1, 'F - test_insert_newline/screen_top')
-  check_eq(Cursor1.line, 2, 'F - test_insert_newline/cursor:line')
-  check_eq(Cursor1.pos, 1, 'F - test_insert_newline/cursor:pos')
-  y = Margin_top
-  App.screen.check(y, 'a', 'F - test_insert_newline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'bc', 'F - test_insert_newline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_insert_newline/screen:3')
-end
-
-function test_insert_from_clipboard()
-  io.write('\ntest_insert_from_clipboard')
-  -- display a few lines with cursor on bottom line
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=2}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_insert_from_clipboard/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_insert_from_clipboard/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_insert_from_clipboard/baseline/screen:3')
-  -- after hitting the enter key the screen scrolls down
-  App.clipboard = 'xy\nz'
-  App.run_after_keychord('C-v')
-  check_eq(Screen_top1.line, 1, 'F - test_insert_from_clipboard/screen_top')
-  check_eq(Cursor1.line, 2, 'F - test_insert_from_clipboard/cursor:line')
-  check_eq(Cursor1.pos, 2, 'F - test_insert_from_clipboard/cursor:pos')
-  y = Margin_top
-  App.screen.check(y, 'axy', 'F - test_insert_from_clipboard/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'zbc', 'F - test_insert_from_clipboard/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_insert_from_clipboard/screen:3')
-end
-
-function test_move_cursor_using_mouse()
-  io.write('\ntest_move_cursor_using_mouse')
-  App.screen.init{width=50, height=60}
-  Lines = load_array{'abc', 'def', 'xyz'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()  -- populate line.y for each line in Lines
-  local screen_left_margin = 25  -- pixels
-  App.run_after_mouserelease(screen_left_margin+8,Margin_top+5, '1')
-  check_eq(Cursor1.line, 1, 'F - test_move_cursor_using_mouse/cursor:line')
-  check_eq(Cursor1.pos, 2, 'F - test_move_cursor_using_mouse/cursor:pos')
-end
-
-function test_pagedown()
-  io.write('\ntest_pagedown')
-  App.screen.init{width=120, height=45}
-  Lines = load_array{'abc', 'def', 'ghi'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  -- initially the first two lines are displayed
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_pagedown/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_pagedown/baseline/screen:2')
-  -- after pagedown the bottom line becomes the top
-  App.run_after_keychord('pagedown')
-  check_eq(Screen_top1.line, 2, 'F - test_pagedown/screen_top')
-  check_eq(Cursor1.line, 2, 'F - test_pagedown/cursor')
-  y = Margin_top
-  App.screen.check(y, 'def', 'F - test_pagedown/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_pagedown/screen:2')
-end
-
-function test_pagedown_skips_drawings()
-  io.write('\ntest_pagedown_skips_drawings')
-  -- some lines of text with a drawing intermixed
-  App.screen.init{width=50, height=80}
-  Lines = load_array{'abc',               -- height 15
-                     '```lines', '```',   -- height 25
-                     'def',               -- height 15
-                     'ghi'}               -- height 15
-  check_eq(Lines[2].mode, 'drawing', 'F - test_pagedown_skips_drawings/baseline/lines')
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  local drawing_height = 20 + App.screen.width / 2  -- default
-  -- initially the screen displays the first line and the drawing
-  -- 15px margin + 15px line1 + 10px margin + 25px drawing + 10px margin = 75px < screen height 80px
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_pagedown_skips_drawings/baseline/screen:1')
-  -- after pagedown the screen draws the drawing up top
-  -- 15px margin + 10px margin + 25px drawing + 10px margin + 15px line3 = 75px < screen height 80px
-  App.run_after_keychord('pagedown')
-  check_eq(Screen_top1.line, 2, 'F - test_pagedown_skips_drawings/screen_top')
-  check_eq(Cursor1.line, 3, 'F - test_pagedown_skips_drawings/cursor')
-  y = Margin_top + drawing_height
-  App.screen.check(y, 'def', 'F - test_pagedown_skips_drawings/screen:1')
-end
-
-function test_pagedown_shows_one_screen_line_in_common()
-  io.write('\ntest_pagedown_shows_one_screen_line_in_common')
-  -- some lines of text with a drawing intermixed
-  App.screen.init{width=50, height=60}
-  Lines = load_array{'abc', 'def ghi jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_pagedown_shows_one_screen_line_in_common/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def ', 'F - test_pagedown_shows_one_screen_line_in_common/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi ', 'F - test_pagedown_shows_one_screen_line_in_common/baseline/screen:3')
-  -- after pagedown the bottom screen line becomes the top
-  App.run_after_keychord('pagedown')
-  check_eq(Screen_top1.line, 2, 'F - test_pagedown_shows_one_screen_line_in_common/screen_top:line')
-  check_eq(Screen_top1.pos, 5, 'F - test_pagedown_shows_one_screen_line_in_common/screen_top:pos')
-  check_eq(Cursor1.line, 2, 'F - test_pagedown_shows_one_screen_line_in_common/cursor:line')
-  check_eq(Cursor1.pos, 5, 'F - test_pagedown_shows_one_screen_line_in_common/cursor:pos')
-  y = Margin_top
-  App.screen.check(y, 'ghi ', 'F - test_pagedown_shows_one_screen_line_in_common/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'jkl', 'F - test_pagedown_shows_one_screen_line_in_common/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'mn', 'F - test_pagedown_shows_one_screen_line_in_common/screen:3')
-end
-
-function test_down_arrow_moves_cursor()
-  io.write('\ntest_down_arrow_moves_cursor')
-  App.screen.init{width=120, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  -- initially the first three lines are displayed
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_down_arrow_moves_cursor/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_down_arrow_moves_cursor/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_down_arrow_moves_cursor/baseline/screen:3')
-  -- after hitting the down arrow, the cursor moves down by 1 line
-  App.run_after_keychord('down')
-  check_eq(Screen_top1.line, 1, 'F - test_down_arrow_moves_cursor/screen_top')
-  check_eq(Cursor1.line, 2, 'F - test_down_arrow_moves_cursor/cursor')
-  -- the screen is unchanged
-  y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_down_arrow_moves_cursor/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_down_arrow_moves_cursor/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_down_arrow_moves_cursor/screen:3')
-end
-
-function test_down_arrow_scrolls_down_by_one_line()
-  io.write('\ntest_down_arrow_scrolls_down_by_one_line')
-  -- display the first three lines with the cursor on the bottom line
-  App.screen.init{width=120, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
-  Line_width = App.screen.width
-  Cursor1 = {line=3, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:3')
-  -- after hitting the down arrow the screen scrolls down by one line
-  App.run_after_keychord('down')
-  check_eq(Screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_line/screen_top')
-  check_eq(Cursor1.line, 4, 'F - test_down_arrow_scrolls_down_by_one_line/cursor')
-  y = Margin_top
-  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_line/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_down_arrow_scrolls_down_by_one_line/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'jkl', 'F - test_down_arrow_scrolls_down_by_one_line/screen:3')
-end
-
-function test_down_arrow_scrolls_down_by_one_screen_line()
-  io.write('\ntest_down_arrow_scrolls_down_by_one_screen_line')
-  -- display the first three lines with the cursor on the bottom line
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=3, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_screen_line/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi ', 'F - test_down_arrow_scrolls_down_by_one_screen_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
-  -- after hitting the down arrow the screen scrolls down by one line
-  App.run_after_keychord('down')
-  check_eq(Screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen_top')
-  check_eq(Cursor1.line, 3, 'F - test_down_arrow_scrolls_down_by_one_screen_line/cursor:line')
-  check_eq(Cursor1.pos, 5, 'F - test_down_arrow_scrolls_down_by_one_screen_line/cursor:pos')
-  y = Margin_top
-  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'ghi ', 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'jkl', 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen:3')
-end
-
-function test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word()
-  io.write('\ntest_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word')
-  -- display the first three lines with the cursor on the bottom line
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghijkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=3, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghijk', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:3')
-  -- after hitting the down arrow the screen scrolls down by one line
-  App.run_after_keychord('down')
-  check_eq(Screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen_top')
-  check_eq(Cursor1.line, 3, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/cursor:line')
-  check_eq(Cursor1.pos, 6, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/cursor:pos')
-  y = Margin_top
-  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'ghijk', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'l', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:3')
-end
-
-function test_page_down_followed_by_down_arrow_does_not_scroll_screen_up()
-  io.write('\ntest_page_down_followed_by_down_arrow_does_not_scroll_screen_up')
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghijkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=3, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghijk', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:3')
-  -- after hitting pagedown the screen scrolls down to start of a long line
-  App.run_after_keychord('pagedown')
-  check_eq(Screen_top1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline2/screen_top')
-  check_eq(Cursor1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline2/cursor:line')
-  check_eq(Cursor1.pos, 1, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline2/cursor:pos')
-  -- after hitting down arrow the screen doesn't scroll down further, and certainly doesn't scroll up
-  App.run_after_keychord('down')
-  check_eq(Screen_top1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen_top')
-  check_eq(Cursor1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/cursor:line')
-  check_eq(Cursor1.pos, 6, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/cursor:pos')
-  y = Margin_top
-  App.screen.check(y, 'ghijk', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'l', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'mno', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen:3')
-end
-
-function test_up_arrow_moves_cursor()
-  io.write('\ntest_up_arrow_moves_cursor')
-  -- display the first 3 lines with the cursor on the bottom line
-  App.screen.init{width=120, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
-  Line_width = 120
-  Cursor1 = {line=3, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_up_arrow_moves_cursor/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_up_arrow_moves_cursor/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_up_arrow_moves_cursor/baseline/screen:3')
-  -- after hitting the up arrow the cursor moves up by 1 line
-  App.run_after_keychord('up')
-  check_eq(Screen_top1.line, 1, 'F - test_up_arrow_moves_cursor/screen_top')
-  check_eq(Cursor1.line, 2, 'F - test_up_arrow_moves_cursor/cursor')
-  -- the screen is unchanged
-  y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_up_arrow_moves_cursor/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_up_arrow_moves_cursor/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_up_arrow_moves_cursor/screen:3')
-end
-
-function test_up_arrow_scrolls_up_by_one_line()
-  io.write('\ntest_up_arrow_scrolls_up_by_one_line')
-  -- display the lines 2/3/4 with the cursor on line 2
-  App.screen.init{width=120, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
-  Line_width = 120
-  Cursor1 = {line=2, pos=1}
-  Screen_top1 = {line=2, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_by_one_line/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_by_one_line/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_by_one_line/baseline/screen:3')
-  -- after hitting the up arrow the screen scrolls up by one line
-  App.run_after_keychord('up')
-  check_eq(Screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_by_one_line/screen_top')
-  check_eq(Cursor1.line, 1, 'F - test_up_arrow_scrolls_up_by_one_line/cursor')
-  y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_by_one_line/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_by_one_line/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_by_one_line/screen:3')
-end
-
-function test_up_arrow_scrolls_up_by_one_screen_line()
-  io.write('\ntest_up_arrow_scrolls_up_by_one_screen_line')
-  -- display lines starting from second screen line of a line
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=3, pos=6}
-  Screen_top1 = {line=3, pos=5}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_by_one_screen_line/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'mno', 'F - test_up_arrow_scrolls_up_by_one_screen_line/baseline/screen:2')
-  -- after hitting the up arrow the screen scrolls up to first screen line
-  App.run_after_keychord('up')
-  y = Margin_top
-  App.screen.check(y, 'ghi ', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'mno', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:3')
-  check_eq(Screen_top1.line, 3, 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen_top')
-  check_eq(Screen_top1.pos, 1, 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen_top')
-  check_eq(Cursor1.line, 3, 'F - test_up_arrow_scrolls_up_by_one_screen_line/cursor:line')
-  check_eq(Cursor1.pos, 1, 'F - test_up_arrow_scrolls_up_by_one_screen_line/cursor:pos')
-end
-
-function test_up_arrow_scrolls_up_to_final_screen_line()
-  io.write('\ntest_up_arrow_scrolls_up_to_final_screen_line')
-  -- display lines starting just after a long line
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc def', 'ghi', 'jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=2, pos=1}
-  Screen_top1 = {line=2, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'mno', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:3')
-  -- after hitting the up arrow the screen scrolls up to final screen line of previous line
-  App.run_after_keychord('up')
-  y = Margin_top
-  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:3')
-  check_eq(Screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen_top')
-  check_eq(Screen_top1.pos, 5, 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen_top')
-  check_eq(Cursor1.line, 1, 'F - test_up_arrow_scrolls_up_to_final_screen_line/cursor:line')
-  check_eq(Cursor1.pos, 5, 'F - test_up_arrow_scrolls_up_to_final_screen_line/cursor:pos')
-end
-
-function test_up_arrow_scrolls_up_to_empty_line()
-  io.write('\ntest_up_arrow_scrolls_up_to_empty_line')
-  -- display a screenful of text with an empty line just above it outside the screen
-  App.screen.init{width=120, height=60}
-  Lines = load_array{'', 'abc', 'def', 'ghi', 'jkl'}
-  Line_width = 120
-  Cursor1 = {line=2, pos=1}
-  Screen_top1 = {line=2, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_to_empty_line/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_empty_line/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_empty_line/baseline/screen:3')
-  -- after hitting the up arrow the screen scrolls up by one line
-  App.run_after_keychord('up')
-  check_eq(Screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_to_empty_line/screen_top')
-  check_eq(Cursor1.line, 1, 'F - test_up_arrow_scrolls_up_to_empty_line/cursor')
-  y = Margin_top
-  -- empty first line
-  y = y + Line_height
-  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_to_empty_line/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_empty_line/screen:3')
-end
-
-function test_pageup()
-  io.write('\ntest_pageup')
-  App.screen.init{width=120, height=45}
-  Lines = load_array{'abc', 'def', 'ghi'}
-  Line_width = App.screen.width
-  Cursor1 = {line=2, pos=1}
-  Screen_top1 = {line=2, pos=1}
-  Screen_bottom1 = {}
-  -- initially the last two lines are displayed
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'def', 'F - test_pageup/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_pageup/baseline/screen:2')
-  -- after pageup the cursor goes to first line
-  App.run_after_keychord('pageup')
-  check_eq(Screen_top1.line, 1, 'F - test_pageup/screen_top')
-  check_eq(Cursor1.line, 1, 'F - test_pageup/cursor')
-  y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_pageup/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_pageup/screen:2')
-end
-
-function test_pageup_scrolls_up_by_screen_line()
-  io.write('\ntest_pageup_scrolls_up_by_screen_line')
-  -- display the first three lines with the cursor on the bottom line
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc def', 'ghi', 'jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=2, pos=1}
-  Screen_top1 = {line=2, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'ghi', 'F - test_pageup_scrolls_up_by_screen_line/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'jkl', 'F - test_pageup_scrolls_up_by_screen_line/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'mno', 'F - test_pageup_scrolls_up_by_screen_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
-  -- after hitting the page-up key the screen scrolls up to top
-  App.run_after_keychord('pageup')
-  check_eq(Screen_top1.line, 1, 'F - test_pageup_scrolls_up_by_screen_line/screen_top')
-  check_eq(Cursor1.line, 1, 'F - test_pageup_scrolls_up_by_screen_line/cursor:line')
-  check_eq(Cursor1.pos, 1, 'F - test_pageup_scrolls_up_by_screen_line/cursor:pos')
-  y = Margin_top
-  App.screen.check(y, 'abc ', 'F - test_pageup_scrolls_up_by_screen_line/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_pageup_scrolls_up_by_screen_line/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_pageup_scrolls_up_by_screen_line/screen:3')
-end
-
-function test_pageup_scrolls_up_from_middle_screen_line()
-  io.write('\ntest_pageup_scrolls_up_from_middle_screen_line')
-  -- display a few lines starting from the middle of a line (Cursor1.pos > 1)
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc def', 'ghi jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=2, pos=5}
-  Screen_top1 = {line=2, pos=5}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'jkl', 'F - test_pageup_scrolls_up_from_middle_screen_line/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'mno', 'F - test_pageup_scrolls_up_from_middle_screen_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
-  -- after hitting the page-up key the screen scrolls up to top
-  App.run_after_keychord('pageup')
-  check_eq(Screen_top1.line, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/screen_top')
-  check_eq(Cursor1.line, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/cursor:line')
-  check_eq(Cursor1.pos, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/cursor:pos')
-  y = Margin_top
-  App.screen.check(y, 'abc ', 'F - test_pageup_scrolls_up_from_middle_screen_line/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_pageup_scrolls_up_from_middle_screen_line/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi ', 'F - test_pageup_scrolls_up_from_middle_screen_line/screen:3')
-end
-
-function test_enter_on_bottom_line_scrolls_down()
-  io.write('\ntest_enter_on_bottom_line_scrolls_down')
-  -- display a few lines with cursor on bottom line
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
-  Line_width = App.screen.width
-  Cursor1 = {line=3, pos=2}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_enter_on_bottom_line_scrolls_down/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_enter_on_bottom_line_scrolls_down/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_enter_on_bottom_line_scrolls_down/baseline/screen:3')
-  -- after hitting the enter key the screen scrolls down
-  App.run_after_keychord('return')
-  check_eq(Screen_top1.line, 2, 'F - test_enter_on_bottom_line_scrolls_down/screen_top')
-  check_eq(Cursor1.line, 4, 'F - test_enter_on_bottom_line_scrolls_down/cursor:line')
-  check_eq(Cursor1.pos, 1, 'F - test_enter_on_bottom_line_scrolls_down/cursor:pos')
-  y = Margin_top
-  App.screen.check(y, 'def', 'F - test_enter_on_bottom_line_scrolls_down/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'g', 'F - test_enter_on_bottom_line_scrolls_down/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'hi', 'F - test_enter_on_bottom_line_scrolls_down/screen:3')
-end
-
-function test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom()
-  io.write('\ntest_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom')
-  -- display just the bottom line on screen
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
-  Line_width = App.screen.width
-  Cursor1 = {line=4, pos=2}
-  Screen_top1 = {line=4, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'jkl', 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/baseline/screen:1')
-  -- after hitting the enter key the screen does not scroll down
-  App.run_after_keychord('return')
-  check_eq(Screen_top1.line, 4, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen_top')
-  check_eq(Cursor1.line, 5, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:line')
-  check_eq(Cursor1.pos, 1, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:pos')
-  y = Margin_top
-  App.screen.check(y, 'j', 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'kl', 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen:2')
-end
-
-function test_position_cursor_on_recently_edited_wrapping_line()
-  -- draw a line wrapping over 2 screen lines
-  io.write('\ntest_position_cursor_on_recently_edited_wrapping_line')
-  App.screen.init{width=120, height=200}
-  Lines = load_array{'abc def ghi jkl mno pqr ', 'xyz'}
-  Line_width = 100
-  Cursor1 = {line=1, pos=25}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  -- I don't understand why 120px fits so much on a fake screen, but whatever..
-  App.screen.check(y, 'abc def ghi ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline1/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'jkl mno pqr ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline1/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'xyz', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline1/screen:3')
-  -- add to the line until it's wrapping over 3 screen lines
-  App.run_after_textinput('s')
-  App.run_after_textinput('t')
-  App.run_after_textinput('u')
-  check_eq(Cursor1.pos, 28, 'F - test_move_cursor_using_mouse/cursor:pos')
-  y = Margin_top
-  App.screen.check(y, 'abc def ghi ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline2/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'jkl mno pqr ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline2/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'stu', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline2/screen:3')
-  -- try to move the cursor earlier in the third screen line by clicking the mouse
-  local screen_left_margin = 25  -- pixels
-  App.run_after_mouserelease(screen_left_margin+8,Margin_top+Line_height*2+5, '1')
-  -- cursor should move
-  check_eq(Cursor1.line, 1, 'F - test_move_cursor_using_mouse/cursor:line')
-  check_eq(Cursor1.pos, 26, 'F - test_move_cursor_using_mouse/cursor:pos')
-end
-
-function test_backspace_can_scroll_up()
-  io.write('\ntest_backspace_can_scroll_up')
-  -- display the lines 2/3/4 with the cursor on line 2
-  App.screen.init{width=120, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
-  Line_width = 120
-  Cursor1 = {line=2, pos=1}
-  Screen_top1 = {line=2, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'def', 'F - test_backspace_can_scroll_up/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_backspace_can_scroll_up/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up/baseline/screen:3')
-  -- after hitting backspace the screen scrolls up by one line
-  App.run_after_keychord('backspace')
-  check_eq(Screen_top1.line, 1, 'F - test_backspace_can_scroll_up/screen_top')
-  check_eq(Cursor1.line, 1, 'F - test_backspace_can_scroll_up/cursor')
-  y = Margin_top
-  App.screen.check(y, 'abcdef', 'F - test_backspace_can_scroll_up/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'ghi', 'F - test_backspace_can_scroll_up/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up/screen:3')
-end
-
-function test_backspace_can_scroll_up_screen_line()
-  io.write('\ntest_backspace_can_scroll_up_screen_line')
-  -- display lines starting from second screen line of a line
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=3, pos=5}
-  Screen_top1 = {line=3, pos=5}
-  Screen_bottom1 = {}
-  App.draw()
-  local y = Margin_top
-  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up_screen_line/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'mno', 'F - test_backspace_can_scroll_up_screen_line/baseline/screen:2')
-  -- after hitting backspace the screen scrolls up by one screen line
-  App.run_after_keychord('backspace')
-  y = Margin_top
-  App.screen.check(y, 'ghijk', 'F - test_backspace_can_scroll_up_screen_line/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'l', 'F - test_backspace_can_scroll_up_screen_line/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'mno', 'F - test_backspace_can_scroll_up_screen_line/screen:3')
-  check_eq(Screen_top1.line, 3, 'F - test_backspace_can_scroll_up_screen_line/screen_top')
-  check_eq(Screen_top1.pos, 1, 'F - test_backspace_can_scroll_up_screen_line/screen_top')
-  check_eq(Cursor1.line, 3, 'F - test_backspace_can_scroll_up_screen_line/cursor:line')
-  check_eq(Cursor1.pos, 4, 'F - test_backspace_can_scroll_up_screen_line/cursor:pos')
-end
-
--- some tests for operating over selections created using Shift- chords
--- we're just testing delete_selection, and it works the same for all keys
-
-function test_backspace_over_selection()
-  io.write('\ntest_backspace_over_selection')
-  -- select just one character within a line with cursor before selection
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=1}
-  Selection1 = {line=1, pos=2}
-  -- backspace deletes the selected character, even though it's after the cursor
-  App.run_after_keychord('backspace')
-  check_eq(Lines[1].data, 'bc', "F - test_backspace_over_selection/data")
-  -- cursor (remains) at start of selection
-  check_eq(Cursor1.line, 1, "F - test_backspace_over_selection/cursor:line")
-  check_eq(Cursor1.pos, 1, "F - test_backspace_over_selection/cursor:pos")
-  -- selection is cleared
-  check_nil(Selection1.line, "F - test_backspace_over_selection/selection")
-end
-
-function test_backspace_over_selection_reverse()
-  io.write('\ntest_backspace_over_selection_reverse')
-  -- select just one character within a line with cursor after selection
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=2}
-  Selection1 = {line=1, pos=1}
-  -- backspace deletes the selected character
-  App.run_after_keychord('backspace')
-  check_eq(Lines[1].data, 'bc', "F - test_backspace_over_selection_reverse/data")
-  -- cursor moves to start of selection
-  check_eq(Cursor1.line, 1, "F - test_backspace_over_selection_reverse/cursor:line")
-  check_eq(Cursor1.pos, 1, "F - test_backspace_over_selection_reverse/cursor:pos")
-  -- selection is cleared
-  check_nil(Selection1.line, "F - test_backspace_over_selection_reverse/selection")
-end
-
-function test_backspace_over_multiple_lines()
-  io.write('\ntest_backspace_over_multiple_lines')
-  -- select just one character within a line with cursor after selection
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=2}
-  Selection1 = {line=4, pos=2}
-  -- backspace deletes the region and joins the remaining portions of lines on either side
-  App.run_after_keychord('backspace')
-  check_eq(Lines[1].data, 'akl', "F - test_backspace_over_multiple_lines/data:1")
-  check_eq(Lines[2].data, 'mno', "F - test_backspace_over_multiple_lines/data:2")
-  -- cursor remains at start of selection
-  check_eq(Cursor1.line, 1, "F - test_backspace_over_multiple_lines/cursor:line")
-  check_eq(Cursor1.pos, 2, "F - test_backspace_over_multiple_lines/cursor:pos")
-  -- selection is cleared
-  check_nil(Selection1.line, "F - test_backspace_over_multiple_lines/selection")
-end
-
-function test_backspace_to_end_of_line()
-  io.write('\ntest_backspace_to_end_of_line')
-  -- select region from cursor to end of line
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=1, pos=2}
-  Selection1 = {line=1, pos=4}
-  -- backspace deletes rest of line without joining to any other line
-  App.run_after_keychord('backspace')
-  check_eq(Lines[1].data, 'a', "F - test_backspace_to_start_of_line/data:1")
-  check_eq(Lines[2].data, 'def', "F - test_backspace_to_start_of_line/data:2")
-  -- cursor remains at start of selection
-  check_eq(Cursor1.line, 1, "F - test_backspace_to_start_of_line/cursor:line")
-  check_eq(Cursor1.pos, 2, "F - test_backspace_to_start_of_line/cursor:pos")
-  -- selection is cleared
-  check_nil(Selection1.line, "F - test_backspace_to_start_of_line/selection")
-end
-
-function test_backspace_to_start_of_line()
-  io.write('\ntest_backspace_to_start_of_line')
-  -- select region from cursor to start of line
-  App.screen.init{width=25+30, height=60}
-  Lines = load_array{'abc', 'def', 'ghi', 'jkl', 'mno'}
-  Line_width = App.screen.width
-  Cursor1 = {line=2, pos=1}
-  Selection1 = {line=2, pos=3}
-  -- backspace deletes beginning of line without joining to any other line
-  App.run_after_keychord('backspace')
-  check_eq(Lines[1].data, 'abc', "F - test_backspace_to_start_of_line/data:1")
-  check_eq(Lines[2].data, 'f', "F - test_backspace_to_start_of_line/data:2")
-  -- cursor remains at start of selection
-  check_eq(Cursor1.line, 2, "F - test_backspace_to_start_of_line/cursor:line")
-  check_eq(Cursor1.pos, 1, "F - test_backspace_to_start_of_line/cursor:pos")
-  -- selection is cleared
-  check_nil(Selection1.line, "F - test_backspace_to_start_of_line/selection")
-end
-
-function test_undo_insert_text()
-  io.write('\ntest_undo_insert_text')
-  App.screen.init{width=120, height=60}
-  Lines = load_array{'abc', 'def', 'xyz'}
-  Line_width = App.screen.width
-  Cursor1 = {line=2, pos=4}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  -- insert a character
-  App.run_after_textinput('g')
-  check_eq(Cursor1.line, 2, 'F - test_undo_insert_text/baseline/cursor:line')
-  check_eq(Cursor1.pos, 5, 'F - test_undo_insert_text/baseline/cursor:pos')
-  check_nil(Selection1.line, 'F - test_undo_insert_text/baseline/selection:line')
-  check_nil(Selection1.pos, 'F - test_undo_insert_text/baseline/selection:pos')
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_undo_insert_text/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'defg', 'F - test_undo_insert_text/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'xyz', 'F - test_undo_insert_text/baseline/screen:3')
-  -- undo
-  App.run_after_keychord('C-z')
-  check_eq(Cursor1.line, 2, 'F - test_undo_insert_text/cursor:line')
-  check_eq(Cursor1.pos, 4, 'F - test_undo_insert_text/cursor:pos')
-  check_nil(Selection1.line, 'F - test_undo_insert_text/selection:line')
-  check_nil(Selection1.pos, 'F - test_undo_insert_text/selection:pos')
-  y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_undo_insert_text/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_undo_insert_text/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'xyz', 'F - test_undo_insert_text/screen:3')
-end
-
-function test_undo_delete_text()
-  io.write('\ntest_undo_delete_text')
-  App.screen.init{width=120, height=60}
-  Lines = load_array{'abc', 'defg', 'xyz'}
-  Line_width = App.screen.width
-  Cursor1 = {line=2, pos=5}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  -- delete a character
-  App.run_after_keychord('backspace')
-  check_eq(Cursor1.line, 2, 'F - test_undo_delete_text/baseline/cursor:line')
-  check_eq(Cursor1.pos, 4, 'F - test_undo_delete_text/baseline/cursor:pos')
-  check_nil(Selection1.line, 'F - test_undo_delete_text/baseline/selection:line')
-  check_nil(Selection1.pos, 'F - test_undo_delete_text/baseline/selection:pos')
-  local y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_undo_delete_text/baseline/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'def', 'F - test_undo_delete_text/baseline/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'xyz', 'F - test_undo_delete_text/baseline/screen:3')
-  -- undo
---?   -- after undo, the backspaced key is selected
-  App.run_after_keychord('C-z')
-  check_eq(Cursor1.line, 2, 'F - test_undo_delete_text/cursor:line')
-  check_eq(Cursor1.pos, 5, 'F - test_undo_delete_text/cursor:pos')
-  check_nil(Selection1.line, 'F - test_undo_delete_text/selection:line')
-  check_nil(Selection1.pos, 'F - test_undo_delete_text/selection:pos')
---?   check_eq(Selection1.line, 2, 'F - test_undo_delete_text/selection:line')
---?   check_eq(Selection1.pos, 4, 'F - test_undo_delete_text/selection:pos')
-  y = Margin_top
-  App.screen.check(y, 'abc', 'F - test_undo_delete_text/screen:1')
-  y = y + Line_height
-  App.screen.check(y, 'defg', 'F - test_undo_delete_text/screen:2')
-  y = y + Line_height
-  App.screen.check(y, 'xyz', 'F - test_undo_delete_text/screen:3')
-end
-
 function Text.compute_fragments(line, line_width)
 --?   print('compute_fragments', line_width)
   line.fragments = {}
diff --git a/text_tests.lua b/text_tests.lua
new file mode 100644
index 0000000..91b3b46
--- /dev/null
+++ b/text_tests.lua
@@ -0,0 +1,931 @@
+-- major tests for text editing flows
+-- This still isn't quite as thorough as I'd like.
+
+function test_draw_text()
+  io.write('\ntest_draw_text')
+  App.screen.init{width=120, height=60}
+  Lines = load_array{'abc', 'def', 'ghi'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_draw_text/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_draw_text/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_draw_text/screen:3')
+end
+
+function test_draw_wrapping_text()
+  io.write('\ntest_draw_wrapping_text')
+  App.screen.init{width=50, height=60}
+  Lines = load_array{'abc', 'defgh', 'xyz'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_draw_wrapping_text/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_draw_wrapping_text/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'gh', 'F - test_draw_wrapping_text/screen:3')
+end
+
+function test_draw_word_wrapping_text()
+  io.write('\ntest_draw_word_wrapping_text')
+  App.screen.init{width=60, height=60}
+  Lines = load_array{'abc def ghi', 'jkl'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc ', 'F - test_draw_word_wrapping_text/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def ', 'F - test_draw_word_wrapping_text/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_draw_word_wrapping_text/screen:3')
+end
+
+function test_draw_text_wrapping_within_word()
+  -- arrange a screen line that needs to be split within a word
+  io.write('\ntest_draw_text_wrapping_within_word')
+  App.screen.init{width=60, height=60}
+  Lines = load_array{'abcd e fghijk', 'xyz'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abcd ', 'F - test_draw_text_wrapping_within_word/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'e fghi', 'F - test_draw_text_wrapping_within_word/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'jk', 'F - test_draw_text_wrapping_within_word/screen:3')
+end
+
+function test_edit_wrapping_text()
+  io.write('\ntest_edit_wrapping_text')
+  App.screen.init{width=50, height=60}
+  Lines = load_array{'abc', 'def', 'xyz'}
+  Line_width = App.screen.width
+  Cursor1 = {line=2, pos=4}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.run_after_textinput('g')
+  App.run_after_textinput('h')
+  App.run_after_textinput('i')
+  App.run_after_textinput('j')
+  App.run_after_textinput('k')
+  App.run_after_textinput('l')
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_edit_wrapping_text/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_edit_wrapping_text/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghij', 'F - test_edit_wrapping_text/screen:3')
+end
+
+function test_insert_newline()
+  io.write('\ntest_insert_newline')
+  -- display a few lines with cursor on bottom line
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=2}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_insert_newline/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_insert_newline/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_insert_newline/baseline/screen:3')
+  -- after hitting the enter key the screen scrolls down
+  App.run_after_keychord('return')
+  check_eq(Screen_top1.line, 1, 'F - test_insert_newline/screen_top')
+  check_eq(Cursor1.line, 2, 'F - test_insert_newline/cursor:line')
+  check_eq(Cursor1.pos, 1, 'F - test_insert_newline/cursor:pos')
+  y = Margin_top
+  App.screen.check(y, 'a', 'F - test_insert_newline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'bc', 'F - test_insert_newline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_insert_newline/screen:3')
+end
+
+function test_insert_from_clipboard()
+  io.write('\ntest_insert_from_clipboard')
+  -- display a few lines with cursor on bottom line
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=2}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_insert_from_clipboard/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_insert_from_clipboard/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_insert_from_clipboard/baseline/screen:3')
+  -- after hitting the enter key the screen scrolls down
+  App.clipboard = 'xy\nz'
+  App.run_after_keychord('C-v')
+  check_eq(Screen_top1.line, 1, 'F - test_insert_from_clipboard/screen_top')
+  check_eq(Cursor1.line, 2, 'F - test_insert_from_clipboard/cursor:line')
+  check_eq(Cursor1.pos, 2, 'F - test_insert_from_clipboard/cursor:pos')
+  y = Margin_top
+  App.screen.check(y, 'axy', 'F - test_insert_from_clipboard/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'zbc', 'F - test_insert_from_clipboard/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_insert_from_clipboard/screen:3')
+end
+
+function test_move_cursor_using_mouse()
+  io.write('\ntest_move_cursor_using_mouse')
+  App.screen.init{width=50, height=60}
+  Lines = load_array{'abc', 'def', 'xyz'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()  -- populate line.y for each line in Lines
+  local screen_left_margin = 25  -- pixels
+  App.run_after_mouserelease(screen_left_margin+8,Margin_top+5, '1')
+  check_eq(Cursor1.line, 1, 'F - test_move_cursor_using_mouse/cursor:line')
+  check_eq(Cursor1.pos, 2, 'F - test_move_cursor_using_mouse/cursor:pos')
+end
+
+function test_pagedown()
+  io.write('\ntest_pagedown')
+  App.screen.init{width=120, height=45}
+  Lines = load_array{'abc', 'def', 'ghi'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  -- initially the first two lines are displayed
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_pagedown/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_pagedown/baseline/screen:2')
+  -- after pagedown the bottom line becomes the top
+  App.run_after_keychord('pagedown')
+  check_eq(Screen_top1.line, 2, 'F - test_pagedown/screen_top')
+  check_eq(Cursor1.line, 2, 'F - test_pagedown/cursor')
+  y = Margin_top
+  App.screen.check(y, 'def', 'F - test_pagedown/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_pagedown/screen:2')
+end
+
+function test_pagedown_skips_drawings()
+  io.write('\ntest_pagedown_skips_drawings')
+  -- some lines of text with a drawing intermixed
+  App.screen.init{width=50, height=80}
+  Lines = load_array{'abc',               -- height 15
+                     '```lines', '```',   -- height 25
+                     'def',               -- height 15
+                     'ghi'}               -- height 15
+  check_eq(Lines[2].mode, 'drawing', 'F - test_pagedown_skips_drawings/baseline/lines')
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  local drawing_height = 20 + App.screen.width / 2  -- default
+  -- initially the screen displays the first line and the drawing
+  -- 15px margin + 15px line1 + 10px margin + 25px drawing + 10px margin = 75px < screen height 80px
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_pagedown_skips_drawings/baseline/screen:1')
+  -- after pagedown the screen draws the drawing up top
+  -- 15px margin + 10px margin + 25px drawing + 10px margin + 15px line3 = 75px < screen height 80px
+  App.run_after_keychord('pagedown')
+  check_eq(Screen_top1.line, 2, 'F - test_pagedown_skips_drawings/screen_top')
+  check_eq(Cursor1.line, 3, 'F - test_pagedown_skips_drawings/cursor')
+  y = Margin_top + drawing_height
+  App.screen.check(y, 'def', 'F - test_pagedown_skips_drawings/screen:1')
+end
+
+function test_pagedown_shows_one_screen_line_in_common()
+  io.write('\ntest_pagedown_shows_one_screen_line_in_common')
+  -- some lines of text with a drawing intermixed
+  App.screen.init{width=50, height=60}
+  Lines = load_array{'abc', 'def ghi jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_pagedown_shows_one_screen_line_in_common/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def ', 'F - test_pagedown_shows_one_screen_line_in_common/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi ', 'F - test_pagedown_shows_one_screen_line_in_common/baseline/screen:3')
+  -- after pagedown the bottom screen line becomes the top
+  App.run_after_keychord('pagedown')
+  check_eq(Screen_top1.line, 2, 'F - test_pagedown_shows_one_screen_line_in_common/screen_top:line')
+  check_eq(Screen_top1.pos, 5, 'F - test_pagedown_shows_one_screen_line_in_common/screen_top:pos')
+  check_eq(Cursor1.line, 2, 'F - test_pagedown_shows_one_screen_line_in_common/cursor:line')
+  check_eq(Cursor1.pos, 5, 'F - test_pagedown_shows_one_screen_line_in_common/cursor:pos')
+  y = Margin_top
+  App.screen.check(y, 'ghi ', 'F - test_pagedown_shows_one_screen_line_in_common/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'jkl', 'F - test_pagedown_shows_one_screen_line_in_common/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'mn', 'F - test_pagedown_shows_one_screen_line_in_common/screen:3')
+end
+
+function test_down_arrow_moves_cursor()
+  io.write('\ntest_down_arrow_moves_cursor')
+  App.screen.init{width=120, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  -- initially the first three lines are displayed
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_down_arrow_moves_cursor/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_down_arrow_moves_cursor/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_down_arrow_moves_cursor/baseline/screen:3')
+  -- after hitting the down arrow, the cursor moves down by 1 line
+  App.run_after_keychord('down')
+  check_eq(Screen_top1.line, 1, 'F - test_down_arrow_moves_cursor/screen_top')
+  check_eq(Cursor1.line, 2, 'F - test_down_arrow_moves_cursor/cursor')
+  -- the screen is unchanged
+  y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_down_arrow_moves_cursor/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_down_arrow_moves_cursor/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_down_arrow_moves_cursor/screen:3')
+end
+
+function test_down_arrow_scrolls_down_by_one_line()
+  io.write('\ntest_down_arrow_scrolls_down_by_one_line')
+  -- display the first three lines with the cursor on the bottom line
+  App.screen.init{width=120, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
+  Line_width = App.screen.width
+  Cursor1 = {line=3, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:3')
+  -- after hitting the down arrow the screen scrolls down by one line
+  App.run_after_keychord('down')
+  check_eq(Screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_line/screen_top')
+  check_eq(Cursor1.line, 4, 'F - test_down_arrow_scrolls_down_by_one_line/cursor')
+  y = Margin_top
+  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_line/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_down_arrow_scrolls_down_by_one_line/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'jkl', 'F - test_down_arrow_scrolls_down_by_one_line/screen:3')
+end
+
+function test_down_arrow_scrolls_down_by_one_screen_line()
+  io.write('\ntest_down_arrow_scrolls_down_by_one_screen_line')
+  -- display the first three lines with the cursor on the bottom line
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=3, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_screen_line/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi ', 'F - test_down_arrow_scrolls_down_by_one_screen_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
+  -- after hitting the down arrow the screen scrolls down by one line
+  App.run_after_keychord('down')
+  check_eq(Screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen_top')
+  check_eq(Cursor1.line, 3, 'F - test_down_arrow_scrolls_down_by_one_screen_line/cursor:line')
+  check_eq(Cursor1.pos, 5, 'F - test_down_arrow_scrolls_down_by_one_screen_line/cursor:pos')
+  y = Margin_top
+  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'ghi ', 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'jkl', 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen:3')
+end
+
+function test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word()
+  io.write('\ntest_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word')
+  -- display the first three lines with the cursor on the bottom line
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghijkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=3, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghijk', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:3')
+  -- after hitting the down arrow the screen scrolls down by one line
+  App.run_after_keychord('down')
+  check_eq(Screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen_top')
+  check_eq(Cursor1.line, 3, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/cursor:line')
+  check_eq(Cursor1.pos, 6, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/cursor:pos')
+  y = Margin_top
+  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'ghijk', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'l', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:3')
+end
+
+function test_page_down_followed_by_down_arrow_does_not_scroll_screen_up()
+  io.write('\ntest_page_down_followed_by_down_arrow_does_not_scroll_screen_up')
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghijkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=3, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghijk', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:3')
+  -- after hitting pagedown the screen scrolls down to start of a long line
+  App.run_after_keychord('pagedown')
+  check_eq(Screen_top1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline2/screen_top')
+  check_eq(Cursor1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline2/cursor:line')
+  check_eq(Cursor1.pos, 1, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline2/cursor:pos')
+  -- after hitting down arrow the screen doesn't scroll down further, and certainly doesn't scroll up
+  App.run_after_keychord('down')
+  check_eq(Screen_top1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen_top')
+  check_eq(Cursor1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/cursor:line')
+  check_eq(Cursor1.pos, 6, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/cursor:pos')
+  y = Margin_top
+  App.screen.check(y, 'ghijk', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'l', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'mno', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen:3')
+end
+
+function test_up_arrow_moves_cursor()
+  io.write('\ntest_up_arrow_moves_cursor')
+  -- display the first 3 lines with the cursor on the bottom line
+  App.screen.init{width=120, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
+  Line_width = 120
+  Cursor1 = {line=3, pos=1}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_up_arrow_moves_cursor/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_up_arrow_moves_cursor/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_up_arrow_moves_cursor/baseline/screen:3')
+  -- after hitting the up arrow the cursor moves up by 1 line
+  App.run_after_keychord('up')
+  check_eq(Screen_top1.line, 1, 'F - test_up_arrow_moves_cursor/screen_top')
+  check_eq(Cursor1.line, 2, 'F - test_up_arrow_moves_cursor/cursor')
+  -- the screen is unchanged
+  y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_up_arrow_moves_cursor/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_up_arrow_moves_cursor/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_up_arrow_moves_cursor/screen:3')
+end
+
+function test_up_arrow_scrolls_up_by_one_line()
+  io.write('\ntest_up_arrow_scrolls_up_by_one_line')
+  -- display the lines 2/3/4 with the cursor on line 2
+  App.screen.init{width=120, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
+  Line_width = 120
+  Cursor1 = {line=2, pos=1}
+  Screen_top1 = {line=2, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_by_one_line/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_by_one_line/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_by_one_line/baseline/screen:3')
+  -- after hitting the up arrow the screen scrolls up by one line
+  App.run_after_keychord('up')
+  check_eq(Screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_by_one_line/screen_top')
+  check_eq(Cursor1.line, 1, 'F - test_up_arrow_scrolls_up_by_one_line/cursor')
+  y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_by_one_line/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_by_one_line/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_by_one_line/screen:3')
+end
+
+function test_up_arrow_scrolls_up_by_one_screen_line()
+  io.write('\ntest_up_arrow_scrolls_up_by_one_screen_line')
+  -- display lines starting from second screen line of a line
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=3, pos=6}
+  Screen_top1 = {line=3, pos=5}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_by_one_screen_line/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'mno', 'F - test_up_arrow_scrolls_up_by_one_screen_line/baseline/screen:2')
+  -- after hitting the up arrow the screen scrolls up to first screen line
+  App.run_after_keychord('up')
+  y = Margin_top
+  App.screen.check(y, 'ghi ', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'mno', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:3')
+  check_eq(Screen_top1.line, 3, 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen_top')
+  check_eq(Screen_top1.pos, 1, 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen_top')
+  check_eq(Cursor1.line, 3, 'F - test_up_arrow_scrolls_up_by_one_screen_line/cursor:line')
+  check_eq(Cursor1.pos, 1, 'F - test_up_arrow_scrolls_up_by_one_screen_line/cursor:pos')
+end
+
+function test_up_arrow_scrolls_up_to_final_screen_line()
+  io.write('\ntest_up_arrow_scrolls_up_to_final_screen_line')
+  -- display lines starting just after a long line
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc def', 'ghi', 'jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=2, pos=1}
+  Screen_top1 = {line=2, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'mno', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:3')
+  -- after hitting the up arrow the screen scrolls up to final screen line of previous line
+  App.run_after_keychord('up')
+  y = Margin_top
+  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:3')
+  check_eq(Screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen_top')
+  check_eq(Screen_top1.pos, 5, 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen_top')
+  check_eq(Cursor1.line, 1, 'F - test_up_arrow_scrolls_up_to_final_screen_line/cursor:line')
+  check_eq(Cursor1.pos, 5, 'F - test_up_arrow_scrolls_up_to_final_screen_line/cursor:pos')
+end
+
+function test_up_arrow_scrolls_up_to_empty_line()
+  io.write('\ntest_up_arrow_scrolls_up_to_empty_line')
+  -- display a screenful of text with an empty line just above it outside the screen
+  App.screen.init{width=120, height=60}
+  Lines = load_array{'', 'abc', 'def', 'ghi', 'jkl'}
+  Line_width = 120
+  Cursor1 = {line=2, pos=1}
+  Screen_top1 = {line=2, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_to_empty_line/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_empty_line/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_empty_line/baseline/screen:3')
+  -- after hitting the up arrow the screen scrolls up by one line
+  App.run_after_keychord('up')
+  check_eq(Screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_to_empty_line/screen_top')
+  check_eq(Cursor1.line, 1, 'F - test_up_arrow_scrolls_up_to_empty_line/cursor')
+  y = Margin_top
+  -- empty first line
+  y = y + Line_height
+  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_to_empty_line/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_empty_line/screen:3')
+end
+
+function test_pageup()
+  io.write('\ntest_pageup')
+  App.screen.init{width=120, height=45}
+  Lines = load_array{'abc', 'def', 'ghi'}
+  Line_width = App.screen.width
+  Cursor1 = {line=2, pos=1}
+  Screen_top1 = {line=2, pos=1}
+  Screen_bottom1 = {}
+  -- initially the last two lines are displayed
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'def', 'F - test_pageup/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_pageup/baseline/screen:2')
+  -- after pageup the cursor goes to first line
+  App.run_after_keychord('pageup')
+  check_eq(Screen_top1.line, 1, 'F - test_pageup/screen_top')
+  check_eq(Cursor1.line, 1, 'F - test_pageup/cursor')
+  y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_pageup/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_pageup/screen:2')
+end
+
+function test_pageup_scrolls_up_by_screen_line()
+  io.write('\ntest_pageup_scrolls_up_by_screen_line')
+  -- display the first three lines with the cursor on the bottom line
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc def', 'ghi', 'jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=2, pos=1}
+  Screen_top1 = {line=2, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'ghi', 'F - test_pageup_scrolls_up_by_screen_line/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'jkl', 'F - test_pageup_scrolls_up_by_screen_line/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'mno', 'F - test_pageup_scrolls_up_by_screen_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
+  -- after hitting the page-up key the screen scrolls up to top
+  App.run_after_keychord('pageup')
+  check_eq(Screen_top1.line, 1, 'F - test_pageup_scrolls_up_by_screen_line/screen_top')
+  check_eq(Cursor1.line, 1, 'F - test_pageup_scrolls_up_by_screen_line/cursor:line')
+  check_eq(Cursor1.pos, 1, 'F - test_pageup_scrolls_up_by_screen_line/cursor:pos')
+  y = Margin_top
+  App.screen.check(y, 'abc ', 'F - test_pageup_scrolls_up_by_screen_line/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_pageup_scrolls_up_by_screen_line/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_pageup_scrolls_up_by_screen_line/screen:3')
+end
+
+function test_pageup_scrolls_up_from_middle_screen_line()
+  io.write('\ntest_pageup_scrolls_up_from_middle_screen_line')
+  -- display a few lines starting from the middle of a line (Cursor1.pos > 1)
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc def', 'ghi jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=2, pos=5}
+  Screen_top1 = {line=2, pos=5}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'jkl', 'F - test_pageup_scrolls_up_from_middle_screen_line/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'mno', 'F - test_pageup_scrolls_up_from_middle_screen_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
+  -- after hitting the page-up key the screen scrolls up to top
+  App.run_after_keychord('pageup')
+  check_eq(Screen_top1.line, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/screen_top')
+  check_eq(Cursor1.line, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/cursor:line')
+  check_eq(Cursor1.pos, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/cursor:pos')
+  y = Margin_top
+  App.screen.check(y, 'abc ', 'F - test_pageup_scrolls_up_from_middle_screen_line/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_pageup_scrolls_up_from_middle_screen_line/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi ', 'F - test_pageup_scrolls_up_from_middle_screen_line/screen:3')
+end
+
+function test_enter_on_bottom_line_scrolls_down()
+  io.write('\ntest_enter_on_bottom_line_scrolls_down')
+  -- display a few lines with cursor on bottom line
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
+  Line_width = App.screen.width
+  Cursor1 = {line=3, pos=2}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_enter_on_bottom_line_scrolls_down/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_enter_on_bottom_line_scrolls_down/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_enter_on_bottom_line_scrolls_down/baseline/screen:3')
+  -- after hitting the enter key the screen scrolls down
+  App.run_after_keychord('return')
+  check_eq(Screen_top1.line, 2, 'F - test_enter_on_bottom_line_scrolls_down/screen_top')
+  check_eq(Cursor1.line, 4, 'F - test_enter_on_bottom_line_scrolls_down/cursor:line')
+  check_eq(Cursor1.pos, 1, 'F - test_enter_on_bottom_line_scrolls_down/cursor:pos')
+  y = Margin_top
+  App.screen.check(y, 'def', 'F - test_enter_on_bottom_line_scrolls_down/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'g', 'F - test_enter_on_bottom_line_scrolls_down/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'hi', 'F - test_enter_on_bottom_line_scrolls_down/screen:3')
+end
+
+function test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom()
+  io.write('\ntest_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom')
+  -- display just the bottom line on screen
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
+  Line_width = App.screen.width
+  Cursor1 = {line=4, pos=2}
+  Screen_top1 = {line=4, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'jkl', 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/baseline/screen:1')
+  -- after hitting the enter key the screen does not scroll down
+  App.run_after_keychord('return')
+  check_eq(Screen_top1.line, 4, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen_top')
+  check_eq(Cursor1.line, 5, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:line')
+  check_eq(Cursor1.pos, 1, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:pos')
+  y = Margin_top
+  App.screen.check(y, 'j', 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'kl', 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen:2')
+end
+
+function test_position_cursor_on_recently_edited_wrapping_line()
+  -- draw a line wrapping over 2 screen lines
+  io.write('\ntest_position_cursor_on_recently_edited_wrapping_line')
+  App.screen.init{width=120, height=200}
+  Lines = load_array{'abc def ghi jkl mno pqr ', 'xyz'}
+  Line_width = 100
+  Cursor1 = {line=1, pos=25}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  -- I don't understand why 120px fits so much on a fake screen, but whatever..
+  App.screen.check(y, 'abc def ghi ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline1/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'jkl mno pqr ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline1/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'xyz', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline1/screen:3')
+  -- add to the line until it's wrapping over 3 screen lines
+  App.run_after_textinput('s')
+  App.run_after_textinput('t')
+  App.run_after_textinput('u')
+  check_eq(Cursor1.pos, 28, 'F - test_move_cursor_using_mouse/cursor:pos')
+  y = Margin_top
+  App.screen.check(y, 'abc def ghi ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline2/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'jkl mno pqr ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline2/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'stu', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline2/screen:3')
+  -- try to move the cursor earlier in the third screen line by clicking the mouse
+  local screen_left_margin = 25  -- pixels
+  App.run_after_mouserelease(screen_left_margin+8,Margin_top+Line_height*2+5, '1')
+  -- cursor should move
+  check_eq(Cursor1.line, 1, 'F - test_move_cursor_using_mouse/cursor:line')
+  check_eq(Cursor1.pos, 26, 'F - test_move_cursor_using_mouse/cursor:pos')
+end
+
+function test_backspace_can_scroll_up()
+  io.write('\ntest_backspace_can_scroll_up')
+  -- display the lines 2/3/4 with the cursor on line 2
+  App.screen.init{width=120, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
+  Line_width = 120
+  Cursor1 = {line=2, pos=1}
+  Screen_top1 = {line=2, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'def', 'F - test_backspace_can_scroll_up/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_backspace_can_scroll_up/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up/baseline/screen:3')
+  -- after hitting backspace the screen scrolls up by one line
+  App.run_after_keychord('backspace')
+  check_eq(Screen_top1.line, 1, 'F - test_backspace_can_scroll_up/screen_top')
+  check_eq(Cursor1.line, 1, 'F - test_backspace_can_scroll_up/cursor')
+  y = Margin_top
+  App.screen.check(y, 'abcdef', 'F - test_backspace_can_scroll_up/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'ghi', 'F - test_backspace_can_scroll_up/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up/screen:3')
+end
+
+function test_backspace_can_scroll_up_screen_line()
+  io.write('\ntest_backspace_can_scroll_up_screen_line')
+  -- display lines starting from second screen line of a line
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=3, pos=5}
+  Screen_top1 = {line=3, pos=5}
+  Screen_bottom1 = {}
+  App.draw()
+  local y = Margin_top
+  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up_screen_line/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'mno', 'F - test_backspace_can_scroll_up_screen_line/baseline/screen:2')
+  -- after hitting backspace the screen scrolls up by one screen line
+  App.run_after_keychord('backspace')
+  y = Margin_top
+  App.screen.check(y, 'ghijk', 'F - test_backspace_can_scroll_up_screen_line/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'l', 'F - test_backspace_can_scroll_up_screen_line/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'mno', 'F - test_backspace_can_scroll_up_screen_line/screen:3')
+  check_eq(Screen_top1.line, 3, 'F - test_backspace_can_scroll_up_screen_line/screen_top')
+  check_eq(Screen_top1.pos, 1, 'F - test_backspace_can_scroll_up_screen_line/screen_top')
+  check_eq(Cursor1.line, 3, 'F - test_backspace_can_scroll_up_screen_line/cursor:line')
+  check_eq(Cursor1.pos, 4, 'F - test_backspace_can_scroll_up_screen_line/cursor:pos')
+end
+
+-- some tests for operating over selections created using Shift- chords
+-- we're just testing delete_selection, and it works the same for all keys
+
+function test_backspace_over_selection()
+  io.write('\ntest_backspace_over_selection')
+  -- select just one character within a line with cursor before selection
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=1}
+  Selection1 = {line=1, pos=2}
+  -- backspace deletes the selected character, even though it's after the cursor
+  App.run_after_keychord('backspace')
+  check_eq(Lines[1].data, 'bc', "F - test_backspace_over_selection/data")
+  -- cursor (remains) at start of selection
+  check_eq(Cursor1.line, 1, "F - test_backspace_over_selection/cursor:line")
+  check_eq(Cursor1.pos, 1, "F - test_backspace_over_selection/cursor:pos")
+  -- selection is cleared
+  check_nil(Selection1.line, "F - test_backspace_over_selection/selection")
+end
+
+function test_backspace_over_selection_reverse()
+  io.write('\ntest_backspace_over_selection_reverse')
+  -- select just one character within a line with cursor after selection
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=2}
+  Selection1 = {line=1, pos=1}
+  -- backspace deletes the selected character
+  App.run_after_keychord('backspace')
+  check_eq(Lines[1].data, 'bc', "F - test_backspace_over_selection_reverse/data")
+  -- cursor moves to start of selection
+  check_eq(Cursor1.line, 1, "F - test_backspace_over_selection_reverse/cursor:line")
+  check_eq(Cursor1.pos, 1, "F - test_backspace_over_selection_reverse/cursor:pos")
+  -- selection is cleared
+  check_nil(Selection1.line, "F - test_backspace_over_selection_reverse/selection")
+end
+
+function test_backspace_over_multiple_lines()
+  io.write('\ntest_backspace_over_multiple_lines')
+  -- select just one character within a line with cursor after selection
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=2}
+  Selection1 = {line=4, pos=2}
+  -- backspace deletes the region and joins the remaining portions of lines on either side
+  App.run_after_keychord('backspace')
+  check_eq(Lines[1].data, 'akl', "F - test_backspace_over_multiple_lines/data:1")
+  check_eq(Lines[2].data, 'mno', "F - test_backspace_over_multiple_lines/data:2")
+  -- cursor remains at start of selection
+  check_eq(Cursor1.line, 1, "F - test_backspace_over_multiple_lines/cursor:line")
+  check_eq(Cursor1.pos, 2, "F - test_backspace_over_multiple_lines/cursor:pos")
+  -- selection is cleared
+  check_nil(Selection1.line, "F - test_backspace_over_multiple_lines/selection")
+end
+
+function test_backspace_to_end_of_line()
+  io.write('\ntest_backspace_to_end_of_line')
+  -- select region from cursor to end of line
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=1, pos=2}
+  Selection1 = {line=1, pos=4}
+  -- backspace deletes rest of line without joining to any other line
+  App.run_after_keychord('backspace')
+  check_eq(Lines[1].data, 'a', "F - test_backspace_to_start_of_line/data:1")
+  check_eq(Lines[2].data, 'def', "F - test_backspace_to_start_of_line/data:2")
+  -- cursor remains at start of selection
+  check_eq(Cursor1.line, 1, "F - test_backspace_to_start_of_line/cursor:line")
+  check_eq(Cursor1.pos, 2, "F - test_backspace_to_start_of_line/cursor:pos")
+  -- selection is cleared
+  check_nil(Selection1.line, "F - test_backspace_to_start_of_line/selection")
+end
+
+function test_backspace_to_start_of_line()
+  io.write('\ntest_backspace_to_start_of_line')
+  -- select region from cursor to start of line
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', 'def', 'ghi', 'jkl', 'mno'}
+  Line_width = App.screen.width
+  Cursor1 = {line=2, pos=1}
+  Selection1 = {line=2, pos=3}
+  -- backspace deletes beginning of line without joining to any other line
+  App.run_after_keychord('backspace')
+  check_eq(Lines[1].data, 'abc', "F - test_backspace_to_start_of_line/data:1")
+  check_eq(Lines[2].data, 'f', "F - test_backspace_to_start_of_line/data:2")
+  -- cursor remains at start of selection
+  check_eq(Cursor1.line, 2, "F - test_backspace_to_start_of_line/cursor:line")
+  check_eq(Cursor1.pos, 1, "F - test_backspace_to_start_of_line/cursor:pos")
+  -- selection is cleared
+  check_nil(Selection1.line, "F - test_backspace_to_start_of_line/selection")
+end
+
+function test_undo_insert_text()
+  io.write('\ntest_undo_insert_text')
+  App.screen.init{width=120, height=60}
+  Lines = load_array{'abc', 'def', 'xyz'}
+  Line_width = App.screen.width
+  Cursor1 = {line=2, pos=4}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  -- insert a character
+  App.run_after_textinput('g')
+  check_eq(Cursor1.line, 2, 'F - test_undo_insert_text/baseline/cursor:line')
+  check_eq(Cursor1.pos, 5, 'F - test_undo_insert_text/baseline/cursor:pos')
+  check_nil(Selection1.line, 'F - test_undo_insert_text/baseline/selection:line')
+  check_nil(Selection1.pos, 'F - test_undo_insert_text/baseline/selection:pos')
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_undo_insert_text/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'defg', 'F - test_undo_insert_text/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'xyz', 'F - test_undo_insert_text/baseline/screen:3')
+  -- undo
+  App.run_after_keychord('C-z')
+  check_eq(Cursor1.line, 2, 'F - test_undo_insert_text/cursor:line')
+  check_eq(Cursor1.pos, 4, 'F - test_undo_insert_text/cursor:pos')
+  check_nil(Selection1.line, 'F - test_undo_insert_text/selection:line')
+  check_nil(Selection1.pos, 'F - test_undo_insert_text/selection:pos')
+  y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_undo_insert_text/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_undo_insert_text/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'xyz', 'F - test_undo_insert_text/screen:3')
+end
+
+function test_undo_delete_text()
+  io.write('\ntest_undo_delete_text')
+  App.screen.init{width=120, height=60}
+  Lines = load_array{'abc', 'defg', 'xyz'}
+  Line_width = App.screen.width
+  Cursor1 = {line=2, pos=5}
+  Screen_top1 = {line=1, pos=1}
+  Screen_bottom1 = {}
+  -- delete a character
+  App.run_after_keychord('backspace')
+  check_eq(Cursor1.line, 2, 'F - test_undo_delete_text/baseline/cursor:line')
+  check_eq(Cursor1.pos, 4, 'F - test_undo_delete_text/baseline/cursor:pos')
+  check_nil(Selection1.line, 'F - test_undo_delete_text/baseline/selection:line')
+  check_nil(Selection1.pos, 'F - test_undo_delete_text/baseline/selection:pos')
+  local y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_undo_delete_text/baseline/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'def', 'F - test_undo_delete_text/baseline/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'xyz', 'F - test_undo_delete_text/baseline/screen:3')
+  -- undo
+--?   -- after undo, the backspaced key is selected
+  App.run_after_keychord('C-z')
+  check_eq(Cursor1.line, 2, 'F - test_undo_delete_text/cursor:line')
+  check_eq(Cursor1.pos, 5, 'F - test_undo_delete_text/cursor:pos')
+  check_nil(Selection1.line, 'F - test_undo_delete_text/selection:line')
+  check_nil(Selection1.pos, 'F - test_undo_delete_text/selection:pos')
+--?   check_eq(Selection1.line, 2, 'F - test_undo_delete_text/selection:line')
+--?   check_eq(Selection1.pos, 4, 'F - test_undo_delete_text/selection:pos')
+  y = Margin_top
+  App.screen.check(y, 'abc', 'F - test_undo_delete_text/screen:1')
+  y = y + Line_height
+  App.screen.check(y, 'defg', 'F - test_undo_delete_text/screen:2')
+  y = y + Line_height
+  App.screen.check(y, 'xyz', 'F - test_undo_delete_text/screen:3')
+end