function test_resize_window()
  App.screen.init{width=300, height=300}
  Editor_state = edit.initialize_test_state()
  Editor_state.filename = 'foo'
  check_eq(App.screen.width, 300, 'baseline/width')
  check_eq(App.screen.height, 300, 'baseline/height')
  check_eq(Editor_state.left, Test_margin_left, 'baseline/left_margin')
  check_eq(Editor_state.right, 300 - Test_margin_right, 'baseline/left_margin')
  App.resize(200, 400)
  -- ugly; resize switches to real, non-test margins
  check_eq(App.screen.width, 200, 'width')
  check_eq(App.screen.height, 400, 'height')
  check_eq(Editor_state.left, Margin_left, 'left_margin')
  check_eq(Editor_state.right, 200-Margin_right, 'right_margin')
  check_eq(Editor_state.width, 200-Margin_left-Margin_right, 'drawing_width')
  -- TODO: how to make assertions about when App.update got past the early exit?
end

function test_drop_file()
  App.screen.init{width=Editor_state.left+300, height=300}
  Editor_state = edit.initialize_test_state()
  App.filesystem['foo'] = 'abc\ndef\nghi\n'
  local fake_dropped_file = {
    opened = false,
    getFilename = function(self)
                    return 'foo'
                  end,
    open = function(self)
             self.opened = true
           end,
    lines = function(self)
              assert(self.opened)
              return App.filesystem['foo']:gmatch('[^\n]+')
            end,
    close = function(self)
              self.opened = false
            end,
  }
  App.filedropped(fake_dropped_file)
  check_eq(#Editor_state.lines, 3, '#lines')
  check_eq(Editor_state.lines[1].data, 'abc', 'lines:1')
  check_eq(Editor_state.lines[2].data, 'def', 'lines:2')
  check_eq(Editor_state.lines[3].data, 'ghi', 'lines:3')
  edit.draw(Editor_state)
end

function test_drop_file_saves_previous()
  App.screen.init{width=Editor_state.left+300, height=300}
  -- initially editing a file called foo that hasn't been saved to filesystem yet
  Editor_state.lines = load_array{'abc', 'def'}
  Editor_state.filename = 'foo'
  schedule_save(Editor_state)
  -- now drag a new file bar from the filesystem
  App.filesystem['bar'] = 'abc\ndef\nghi\n'
  local fake_dropped_file = {
    opened = false,
    getFilename = function(self)
                    return 'bar'
                  end,
    open = function(self)
             self.opened = true
           end,
    lines = function(self)
              assert(self.opened)
              return App.filesystem['bar']:gmatch('[^\n]+')
            end,
    close = function(self)
              self.opened = false
            end,
  }
  App.filedropped(fake_dropped_file)
  -- filesystem now contains a file called foo
  check_eq(App.filesystem['foo'], 'abc\ndef\n', 'check')
end