### writing tests
* `App.screen.init{width=.., height=..}` -- creates a fake screen for a test
* `App.screen.check(y, expected_contents, msg)` -- verifies text written to
  the fake screen at `y`. This isn't very realistic; `y` must exactly match
  what was displayed, and the expected contents show everything printed to
  that `y` in chronological order, regardless of `x` coordinate. In spite of
  these limitations, you can write lots of useful tests with this.
* `App.run_after_textinput(t)` -- mimics keystrokes resulting in `t` and then
  draws one frame.
* `App.run_after_keychord(chord)` -- mimics keystrokes resulting in `chord`
  and then draws one frame.
* `App.run_after_mouse_press(x,y, mouse_button)` -- mimics a mouse press down
  followed by drawing a frame.
* `App.run_after_mouse_release(x,y, mouse_button)` -- mimics a mouse release
  up followed by drawing a frame.
* `App.run_after_mouse_click(x,y, mouse_button)` -- mimics a mouse press down
  and mouse release up followed by drawing a frame.
* `App.wait_fake_time(t)` -- simulates the passage of time for `App.getTime()`.

  App.screen.init({width=100, height=50})

  App.screen.init{width=100, height=50}