run routine f with a keyboard channel containing #\a and a fake screen

check that fake screen contains 'a' at (5, 5)

---

; At its core, an editor is a 2D array of characters and a cursor.

given [
  editor 5 5
]

Cursor should be at (0 0)

now [
  type "abc"
]

Cursor should be at (0 3)
"abc" should be at (0 0)
Trace should contain [
  typed "a"
  typed "b"
  typed "c"
]

---

Extract unit tests for helper out of all existing tests.