check_eq(Editor_state.cursor1.line, 1, '1/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, '1/cursor:pos')
end
  check_eq(Editor_state.cursor1.line, 1, '1/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, '1/cursor:pos')
end
function test_search_wrap_upwards()
  check_eq(Editor_state.cursor1.line, 1, '2/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, '2/cursor:pos')
end
function test_search_wrap()
  check_eq(Editor_state.cursor1.line, 4, '2/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, '2/cursor:pos')
end
function test_search_upwards()
  check_eq(Editor_state.cursor1.line, 2, '1/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, '1/cursor:pos')
  -- reset cursor
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- search for second occurrence
  edit.run_after_keychord(Editor_state, 'C-f')
  check_eq(Editor_state.selection1.line, 1, 'line')
  check_eq(Editor_state.selection1.pos, 2, 'pos')
end
  check_eq(Editor_state.lines[1].data, 'xbc', 'baseline')
  check_nil(Editor_state.selection1.line, 'baseline:selection')
  -- undo
  edit.run_after_keychord(Editor_state, 'C-z')
  edit.run_after_keychord(Editor_state, 'C-z')
  -- selection is restored
  App.screen.check(y, 'xyz', 'screen:3')
end
  App.screen.check(y, 'defg', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'cursor:pos')
  check_nil(Editor_state.selection1.line, 'selection:line')
  check_nil(Editor_state.selection1.pos, 'selection:pos')
--?   check_eq(Editor_state.selection1.line, 2, 'selection:line')
--?   check_eq(Editor_state.selection1.pos, 4, 'selection:pos')
  y = Editor_state.top
  App.screen.check(y, 'xyz', 'baseline/screen:3')
  -- undo
--?   -- after undo, the backspaced key is selected
  edit.run_after_keychord(Editor_state, 'C-z')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.cursor1.line, 2, 'baseline/cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'baseline/cursor:pos')
  check_nil(Editor_state.selection1.line, 'baseline/selection:line')
  check_nil(Editor_state.selection1.pos, 'baseline/selection:pos')
  local y = Editor_state.top
  App.screen.check(y, 'xyz', 'screen:3')
end
function test_undo_delete_text()
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'cursor:pos')
  check_nil(Editor_state.selection1.line, 'selection:line')
  check_nil(Editor_state.selection1.pos, 'selection:pos')
  y = Editor_state.top
  App.screen.check(y, 'xyz', 'baseline/screen:3')
  -- undo
  edit.run_after_keychord(Editor_state, 'C-z')
  App.screen.check(y, 'defg', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.cursor1.line, 2, 'baseline/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'baseline/cursor:pos')
  check_nil(Editor_state.selection1.line, 'baseline/selection:line')
  check_nil(Editor_state.selection1.pos, 'baseline/selection:pos')
  local y = Editor_state.top
  check_nil(Editor_state.selection1.line, 'selection')
end
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  -- selection is cleared
  check_eq(Editor_state.lines[1].data, 'abc', 'data:1')
  check_eq(Editor_state.lines[2].data, 'f', 'data:2')
  -- cursor remains at start of selection
  check_nil(Editor_state.selection1.line, 'selection')
end
function test_backspace_to_start_of_line()
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
  -- selection is cleared
  check_eq(Editor_state.lines[1].data, 'a', 'data:1')
  check_eq(Editor_state.lines[2].data, 'def', 'data:2')
  -- cursor remains at start of selection
  check_nil(Editor_state.selection1.line, 'selection')
end
function test_backspace_to_end_of_line()
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
  -- selection is cleared
  check_eq(Editor_state.lines[1].data, 'akl', 'data:1')
  check_eq(Editor_state.lines[2].data, 'mno', 'data:2')
  -- cursor remains at start of selection
  check_nil(Editor_state.selection1.line, 'selection')
end
function test_backspace_over_multiple_lines()
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  -- selection is cleared
  check_eq(Editor_state.lines[1].data, 'bc', 'data')
  -- cursor moves to start of selection
  check_nil(Editor_state.selection1.line, 'selection')
end
function test_backspace_over_selection_reverse()
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  -- selection is cleared
  check_eq(Editor_state.lines[1].data, 'bc', 'data')
  -- cursor (remains) at start of selection
  check_eq(Editor_state.lines[1].data, 'abcdef', 'check')
end
  App.screen.check(y, 'mno', 'screen:3')
  check_eq(Editor_state.screen_top1.line, 3, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 1, 'screen_top:pos')
  check_eq(Editor_state.cursor1.line, 3, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'cursor:pos')
end
function test_backspace_past_line_boundary()
  App.screen.check(y, 'kl', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghij', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'baseline/screen:2')
  -- after hitting backspace the screen scrolls up by one screen line
  edit.run_after_keychord(Editor_state, 'backspace')
  y = Editor_state.top
  App.screen.check(y, 'jkl', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'screen:3')
end
function test_backspace_can_scroll_up_screen_line()
  App.screen.check(y, 'ghi', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abcdef', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')
  y = Editor_state.top
  App.screen.check(y, 'jkl', 'baseline/screen:3')
  -- after hitting backspace the screen scrolls up by one line
  edit.run_after_keychord(Editor_state, 'backspace')
  App.screen.check(y, 'ghi', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 26, 'cursor:pos')
end
function test_backspace_can_scroll_up()
  App.screen.check(y, 'stu', 'baseline2/screen:3')
  -- try to move the cursor earlier in the third screen line by clicking the mouse
  App.screen.check(y, 'jkl mno pqr ', 'baseline2/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc def ghi ', 'baseline2/screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.cursor1.pos, 28, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'xyz', 'baseline1/screen:3')
  -- add to the line until it's wrapping over 3 screen lines
  App.screen.check(y, 'jkl mno pqr ', 'baseline1/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc def ghi ', 'baseline1/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'screen:3')
end
function test_position_cursor_on_recently_edited_wrapping_line()
  -- draw a line wrapping over 2 screen lines
  App.screen.check(y, 'ghi ', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 8, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'ghi ', 'baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting end the screen scrolls down by one line
  edit.run_after_keychord(Editor_state, 'end')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'screen:3')
  check_eq(Editor_state.screen_top1.line, 3, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 1, 'screen_top:pos')
  check_eq(Editor_state.cursor1.line, 3, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
end
function test_end_scrolls_down_in_wrapped_line()
  App.screen.check(y, 'jkl', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'baseline/screen:2')
  -- after hitting home the screen scrolls up to first screen line
  edit.run_after_keychord(Editor_state, 'home')
  y = Editor_state.top
  App.screen.check(y, 'jkl', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'screen:3')
end
function test_home_scrolls_up_in_wrapped_line()
  App.screen.check(y, 'ghi ', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 6, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'ghi ', 'baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting the right arrow the screen scrolls down by one line
  edit.run_after_keychord(Editor_state, 'right')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'screen:3')
  check_eq(Editor_state.screen_top1.line, 3, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 1, 'screen_top:pos')
  check_eq(Editor_state.cursor1.line, 3, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'cursor:pos')
end
function test_right_arrow_scrolls_down_in_wrapped_line()
  App.screen.check(y, 'jkl', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'baseline/screen:2')
  -- after hitting the left arrow the screen scrolls up to first screen line
  edit.run_after_keychord(Editor_state, 'left')
  y = Editor_state.top
  App.screen.check(y, 'jkl', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'kl', 'screen:3')
end
function test_left_arrow_scrolls_up_in_wrapped_line()
  App.screen.check(y, 'ghij', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 7, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'ghi', 'baseline/screen:3')
  -- after typing something the line wraps and the screen scrolls down
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'a', 'screen:1')
end
function test_typing_on_bottom_line_scrolls_down()
  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
  local y = Editor_state.top
  App.screen.check(y, 'kl', 'screen:2')
end
function test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom()
  App.screen.check(y, 'j', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 4, 'screen_top')
  check_eq(Editor_state.cursor1.line, 5, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'jkl', 'baseline/screen:1')
  -- after hitting the enter key the screen does not scroll down
  edit.run_after_keychord(Editor_state, 'return')
  App.screen.check(y, 'hi', 'screen:3')
end
function test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom()
  App.screen.check(y, 'g', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 4, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'ghi', 'baseline/screen:3')
  -- after hitting the enter key the screen scrolls down
  edit.run_after_keychord(Editor_state, 'return')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'screen:3')
end
function test_enter_on_bottom_line_scrolls_down()
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc ', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'mno', 'baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting the page-up key the screen scrolls up to top
  edit.run_after_keychord(Editor_state, 'pageup')
  App.screen.check(y, 'jkl', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:3')
end
function test_pageup_scrolls_up_from_middle_screen_line()
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc ', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'mno', 'baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting the page-up key the screen scrolls up to top
  edit.run_after_keychord(Editor_state, 'pageup')
  App.screen.check(y, 'jkl', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:2')
end
function test_pageup_scrolls_up_by_screen_line()
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')
  y = Editor_state.top
  App.screen.check(y, 'ghi', 'baseline/screen:2')
  -- after pageup the cursor goes to first line
  edit.run_after_keychord(Editor_state, 'pageup')
  App.screen.check(y, 'def', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:3')
end
function test_pageup()
  App.screen.check(y, 'abc', 'screen:2')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')
  y = Editor_state.top
  -- empty first line
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:3')
  -- after hitting the up arrow the screen scrolls up by one line
  edit.run_after_keychord(Editor_state, 'up')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'screen:3')
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 5, 'screen_top:pos')
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'cursor:pos')
end
function test_up_arrow_scrolls_up_to_empty_line()
  App.screen.check(y, 'ghi', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'baseline/screen:3')
  -- after hitting the up arrow the screen scrolls up to final screen line of previous line
  edit.run_after_keychord(Editor_state, 'up')
  y = Editor_state.top
  App.screen.check(y, 'jkl', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'screen:3')
  check_eq(Editor_state.screen_top1.line, 3, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 1, 'screen_top:pos')
  check_eq(Editor_state.cursor1.line, 3, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
end
function test_up_arrow_scrolls_up_to_final_screen_line()
  App.screen.check(y, 'jkl', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'baseline/screen:2')
  -- after hitting the up arrow the screen scrolls up to first screen line
  edit.run_after_keychord(Editor_state, 'up')
  y = Editor_state.top
  App.screen.check(y, 'jkl', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:3')
end
function test_up_arrow_scrolls_up_by_one_screen_line()
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')
  y = Editor_state.top
  App.screen.check(y, 'jkl', 'baseline/screen:3')
  -- after hitting the up arrow the screen scrolls up by one line
  edit.run_after_keychord(Editor_state, 'up')
  App.screen.check(y, 'ghi', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:3')
end
function test_up_arrow_scrolls_up_by_one_line()
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'cursor')
  -- the screen is unchanged
  y = Editor_state.top
  App.screen.check(y, 'ghi', 'baseline/screen:3')
  -- after hitting the up arrow the cursor moves up by 1 line
  edit.run_after_keychord(Editor_state, 'up')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'screen:3')
end
function test_up_arrow_moves_cursor()
  App.screen.check(y, 'kl', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghij', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 3, 'screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'cursor:pos')
  y = Editor_state.top
  check_eq(Editor_state.screen_top1.line, 3, 'baseline2/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'baseline2/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'baseline2/cursor:pos')
  -- after hitting down arrow the screen doesn't scroll down further, and certainly doesn't scroll up
  edit.run_after_keychord(Editor_state, 'down')
  App.screen.check(y, 'ghij', 'baseline/screen:3')
  -- after hitting pagedown the screen scrolls down to start of a long line
  edit.run_after_keychord(Editor_state, 'pagedown')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'kl', 'screen:3')
end
  App.screen.check(y, 'ghij', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'ghij', 'baseline/screen:3')
  -- after hitting the down arrow the screen scrolls down by one line
  edit.run_after_keychord(Editor_state, 'down')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'screen:3')
end
function test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word()
  App.screen.check(y, 'ghi ', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'ghi ', 'baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting the down arrow the screen scrolls down by one line
  edit.run_after_keychord(Editor_state, 'down')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'screen:3')
end
function test_down_arrow_scrolls_down_by_one_screen_line()
  App.screen.check(y, 'ghi', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 4, 'cursor')
  y = Editor_state.top
  App.screen.check(y, 'ghi', 'baseline/screen:3')
  -- after hitting the down arrow the screen scrolls down by one line
  edit.run_after_keychord(Editor_state, 'down')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:3')
end
function test_down_arrow_scrolls_down_by_one_line()
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'cursor')
  -- the screen is unchanged
  y = Editor_state.top
  App.screen.check(y, 'ghi', 'baseline/screen:3')
  -- after hitting the down arrow, the cursor moves down by 1 line
  edit.run_after_keychord(Editor_state, 'down')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 9, 'screen_top:pos')
end
function test_down_arrow_moves_cursor()
  App.screen.check(y, 'mno ', 'screen:3')
end
function test_pagedown_never_moves_up()
  App.screen.check(y, 'jkl ', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi ', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 9, 'screen_top:pos')
  y = Editor_state.top
  App.screen.check(y, 'ghi ', 'baseline/screen:3')
  -- after pagedown we scroll down the very long wrapping line
  edit.run_after_keychord(Editor_state, 'pagedown')
  App.screen.check(y, 'def ', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc ', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:1')
end
function test_pagedown_can_start_from_middle_of_long_wrapping_line()
  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'cursor')
  y = Editor_state.top + drawing_height
  App.screen.check(y, 'abc', '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
  edit.run_after_keychord(Editor_state, 'pagedown')
  check_eq(Editor_state.lines[2].mode, 'drawing', 'baseline/lines')
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  local drawing_height = Drawing_padding_height + drawing_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
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'ghi', 'screen:2')
end
function test_pagedown_skips_drawings()
  App.screen.check(y, 'def', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'cursor')
  y = Editor_state.top
  App.screen.check(y, 'def', 'baseline/screen:2')
  -- after pagedown the bottom line becomes the top
  edit.run_after_keychord(Editor_state, 'pagedown')
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  check_nil(Editor_state.selection1.line, 'check')
end
  check_eq(Editor_state.selection1.line, 1, 'selection:line')
  check_eq(Editor_state.selection1.pos, 2, 'selection:pos')
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
end
  check_eq(Editor_state.selection1.line, 1, 'selection:line')
  check_eq(Editor_state.selection1.pos, 2, 'selection:pos')
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'cursor:pos')
end
function test_select_text_repeatedly_using_mouse_and_shift()
  check_eq(Editor_state.selection1.line, 1, 'selection:line')
  check_eq(Editor_state.selection1.pos, 2, 'selection:pos')
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'cursor:pos')
end
function test_select_text_using_mouse_and_shift()
  App.screen.check(y, 'def', 'screen:3')
end
function test_select_text_using_mouse()
  App.screen.check(y, 'zbc', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'axy', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'ghi', 'baseline/screen:3')
  -- paste some text including a newline, check that new line is created
  App.clipboard = 'xy\nz'
  edit.run_after_keychord(Editor_state, 'C-v')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  check_eq(Editor_state.lines[1].data, '', 'data:1')
  check_eq(Editor_state.lines[2].data, 'abc', 'data:2')
end
function test_insert_from_clipboard()
  App.screen.check(y, 'def', 'screen:3')
end
function test_insert_newline_at_start_of_line()
  App.screen.check(y, 'bc', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'a', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'ghi', 'baseline/screen:3')
  -- hitting the enter key splits the line
  edit.run_after_keychord(Editor_state, 'return')
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'fg', 'screen:3')
end
function test_insert_newline()
  App.screen.check(y, 'de', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.screen_top1.line, 1, 'check')
  check_eq(Editor_state.lines[1].data, 'ahi', 'data')
end
  App.screen.check(y, 'jkl', 'baseline/screen:3')
  -- set up a selection starting above the currently displayed page
  Editor_state.selection1 = {line=1, pos=2}
  -- delete selection
  edit.run_after_keychord(Editor_state, 'backspace')
  -- page scrolls up
  App.screen.check(y, 'ghi', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.lines[1].data, 'xyzdef', 'check')
end
function test_deleting_selection_may_scroll()
  check_eq(Editor_state.lines[1].data, 'bc', 'data')
end
function test_paste_replaces_selection()
  check_eq(App.clipboard, 'a', 'clipboard')
  -- selected text is deleted
  check(Editor_state.selection1.line, 'check')
end
function test_cut()
  check_eq(App.clipboard, 'a', 'clipboard')
  -- selection is reset since shift key is not pressed
  check_nil(Editor_state.selection1.line, 'check')
  check_eq(Editor_state.lines[1].data, 'Dbc', 'data')
end
function test_copy_does_not_reset_selection()
  check_eq(Editor_state.lines[1].data, 'xbc', 'check')
end
function test_edit_with_shift_key_deletes_selection()
  check_nil(Editor_state.selection1.line, 'check')
  check_eq(Editor_state.lines[1].data, 'abc', 'data')
end
  check_eq(Editor_state.selection1.line, 1, 'selection:line')
  check_eq(Editor_state.selection1.pos, 1, 'selection:pos')
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
end
function test_cursor_movement_without_shift_resets_selection()
  check_eq(Editor_state.cursor1.pos, 20, 'cursor')
end
function test_select_text()
  App.screen.check(y, 'the quick brown fox ', 'baseline/screen:1')
  y = y + Editor_state.line_height
  -- click past the end of the screen line
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  -- cursor moves to end of screen line
  check_eq(Editor_state.cursor1.pos, 15, 'cursor')  -- one more than the number of UTF-8 code-points
end
function test_click_past_end_of_word_wrapping_line()
  App.screen.check(y, 'am', 'baseline/screen:3')
  y = y + Editor_state.line_height
  -- click past the end of it
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  -- cursor moves to end of line
  App.screen.check(y, 'I’m ad', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'madam ', 'baseline/screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.cursor1.pos, 15, 'cursor')  -- one more than the number of UTF-8 code-points
end
function test_click_past_end_of_wrapping_line_containing_non_ascii()
  App.screen.check(y, 'am', 'baseline/screen:3')
  y = y + Editor_state.line_height
  -- click past the end of it
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  -- cursor moves to end of line
  App.screen.check(y, "I'm ad", 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'madam ', 'baseline/screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 12, 'cursor:pos')
end
function test_click_past_end_of_wrapping_line()
  App.screen.check(y, "I'm ad", 'baseline/screen:2')
  y = y + Editor_state.line_height
  -- click past end of second screen line
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  -- cursor moves to end of screen line
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 12, 'cursor:pos')
end
function test_click_on_wrapping_line_rendered_from_partway_at_top_of_screen()
  App.screen.check(y, "I'm ad", 'baseline/screen:2')
  y = y + Editor_state.line_height
  -- click past end of second screen line
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  -- cursor moves to end of screen line
  App.screen.check(y, 'madam ', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, '’m a', 'screen:3')
end
function test_click_on_wrapping_line()
  App.screen.check(y, 'am I', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mad', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ijk', 'screen:3')
end
function test_draw_wrapping_text_containing_non_ascii()
  -- draw a long line containing non-ASCII
  App.screen.check(y, 'e fgh', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abcd ', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
  check_nil(Editor_state.selection1.line, 'selection is empty to avoid perturbing future edits')
end
function test_draw_text_wrapping_within_word()
  -- arrange a screen line that needs to be split within a word
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
  check_nil(Editor_state.selection1.line, 'selection is empty to avoid perturbing future edits')
end
  App.screen.check(y, 'ghi', 'screen:3')
end
  App.screen.check(y, 'def ', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc ', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'fgh', 'screen:3')
end
function test_draw_word_wrapping_text()
  App.screen.check(y, 'de', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:3')
end
function test_draw_wrapping_text()
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  check_eq(Editor_state.cursor1.line, 1, 'cursor')
end
function test_draw_text()
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
  check_nil(Editor_state.selection1.line, 'selection is empty to avoid perturbing future edits')
end
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  check_nil(Editor_state.selection1.line, 'selection is empty to avoid perturbing future edits')
end
  check_nil(Editor_state.selection1.line, 'selection:line')
  check_nil(Editor_state.selection1.pos, 'selection:pos')
end
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
  -- selection is empty to avoid perturbing future edits
  check_eq(Editor_state.cursor1.line, 2, 'line')
  check_eq(Editor_state.cursor1.pos, 4, 'pos')
end
  check_eq(Editor_state.cursor1.pos, 9, 'check')
end
function test_move_past_end_of_word_on_next_line()
  check_eq(Editor_state.cursor1.pos, 4, 'check')
end
function test_skip_multiple_spaces_to_next_word()
  check_eq(Editor_state.cursor1.pos, 8, 'check')
end
function test_skip_past_tab_to_next_word()
  check_eq(Editor_state.cursor1.pos, 4, 'check')
end
function test_skip_to_next_word()
  check_eq(Editor_state.cursor1.line, 1, 'line')
  check_eq(Editor_state.cursor1.pos, 5, 'pos')
end
function test_move_past_end_of_word()
  check_eq(Editor_state.cursor1.pos, 1, 'check')
end
function test_move_to_start_of_word_on_previous_line()
  check_eq(Editor_state.cursor1.pos, 9, 'check')
end
function test_skip_multiple_spaces_to_previous_word()
  check_eq(Editor_state.cursor1.pos, 1, 'check')
end
function test_skip_past_tab_to_previous_word()
  check_eq(Editor_state.cursor1.pos, 1, 'check')
end
function test_skip_to_previous_word()
  check_eq(Editor_state.cursor1.pos, 1, 'check')
end
function test_move_to_start_of_previous_word()
  check_eq(Editor_state.cursor1.line, 2, 'line')
  check_eq(Editor_state.cursor1.pos, 1, 'pos')
end
function test_move_to_start_of_word()
  check_eq(Editor_state.cursor1.line, 1, 'line')
  check_eq(Editor_state.cursor1.pos, 4, 'pos')  -- past end of line
end
function test_move_right_to_next_line()
  check_eq(Editor_state.cursor1.pos, 2, 'check')
end
function test_move_left_to_previous_line()
  check_eq(Editor_state.cursor1.pos, 1, 'check')
end
function test_move_right()
  App.screen.check(y, 'a', 'screen:1')
end
function test_press_ctrl()
  check_eq(#Editor_state.lines, 1, '#lines')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
end
function test_insert_first_character()
  check_eq(#Editor_state.lines, 1, '#lines')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')
end
function test_backspace_from_start_of_final_line()
  check_eq(#Editor_state.lines, 2, '#lines')
  check_eq(Editor_state.cursor1.line, 2, 'cursor')
end
function test_backspace_to_delete_drawing()
  check_eq(#Editor_state.lines, 1, '#lines')
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 1, 'screen_top:pos')
end
function test_click_to_create_drawing()

  check_eq(App.filesystem['foo'], 'abc\ndef\n', 'check')
end
  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()
  check_eq(Editor_state.left, Margin_left, 'edit:left')
  check_eq(Editor_state.right, App.screen.width/2 - Margin_right, 'edit:right')
  check_eq(Log_browser_state.left, App.screen.width/2 + Margin_left, 'log:left')
  check_eq(Log_browser_state.right, App.screen.width - Margin_right, 'log:right')
end
  check_eq(Log_browser_state.left, App.screen.width/2 + Margin_left, 'log:left')
  check_eq(Log_browser_state.right, App.screen.width - Margin_right, 'log:right')
end
function test_show_log_browser_side_resizes_both_sides_if_cannot_double_window_width()
  check_eq(Editor_state.left, Margin_left, 'edit:left')
  check_eq(Editor_state.right, old_editor_right, 'edit:right')
  -- log browser margins are adjusted
  check_eq(App.screen.width, 600, 'display:width')
  -- left side margins are unchanged
  check(Show_log_browser_side, 'check')
end
  check(not Show_log_browser_side, 'baseline')
  -- pressing ctrl+l shows log-browser side
  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?
  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/right_margin')
  App.resize(200, 400)

  check_eq(#Editor_state.lines, 1, '#lines')
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 1, 'screen_top:pos')

  check_eq(#Editor_state.lines, 2, '#lines')
  check_eq(Editor_state.cursor1.line, 2, 'cursor')
  check_eq(#Editor_state.lines, 1, '#lines')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')

  check_eq(Editor_state.lines[1].data, 'abc', 'F - test_cursor_movement_without_shift_resets_selection/data')

  check_eq(Editor_state.lines[1].data, 'xbc', 'F - test_edit_deletes_selection')

  check_eq(Editor_state.lines[1].data, 'Dbc', 'F - test_edit_with_shift_key_deletes_selection/data')

  check_eq(Editor_state.lines[1].data, 'bc', 'F - test_cut/data')

  check_eq(Editor_state.lines[1].data, 'xyzdef', 'F - test_paste_replaces_selection')

  check_eq(Editor_state.lines[1].data, 'ahi', 'F - test_deleting_selection_may_scroll/data')

  check_eq(Editor_state.lines[1].data, '', 'F - test_insert_newline_at_start_of_line/data:1')
  check_eq(Editor_state.lines[2].data, 'abc', 'F - test_insert_newline_at_start_of_line/data:2')

  App.screen.check(y, 'ghi', 'screen:2')

  check_eq(Editor_state.lines[2].mode, 'drawing', 'baseline/lines')
  App.screen.check(y, 'abc', 'baseline/screen:1')
  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'cursor')
  App.screen.check(y, 'def', 'screen:1')

  check_eq(Editor_state.lines[1].data, 'abcdef', "F - test_backspace_past_line_boundary")

  check_eq(Editor_state.lines[1].data, 'bc', "F - test_backspace_over_selection/data")

  check_eq(Editor_state.lines[1].data, 'bc', "F - test_backspace_over_selection_reverse/data")

  check_eq(Editor_state.lines[1].data, 'akl', "F - test_backspace_over_multiple_lines/data:1")
  check_eq(Editor_state.lines[2].data, 'mno', "F - test_backspace_over_multiple_lines/data:2")

  check_eq(Editor_state.lines[1].data, 'a', "F - test_backspace_to_start_of_line/data:1")
  check_eq(Editor_state.lines[2].data, 'def', "F - test_backspace_to_start_of_line/data:2")

  check_eq(Editor_state.lines[1].data, 'abc', "F - test_backspace_to_start_of_line/data:1")
  check_eq(Editor_state.lines[2].data, 'f', "F - test_backspace_to_start_of_line/data:2")

  check_eq(Editor_state.lines[1].data, 'xbc', 'F - test_undo_restores_selection/baseline')

  check_eq(Editor_state.lines[1].data, 'xbc', 'baseline')
  check_nil(Editor_state.selection1.line, 'baseline:selection')

  io.write('\ntest_initial_state')

  check_eq(#Editor_state.lines, 1, 'F - test_initial_state/#lines')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_initial_state/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_initial_state/cursor:pos')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_initial_state/screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 1, 'F - test_initial_state/screen_top:pos')

  check_eq(#Editor_state.lines, 1, '#lines')
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 1, 'screen_top:pos')

  io.write('\ntest_click_to_create_drawing')

  check_eq(#Editor_state.lines, 2, 'F - test_click_to_create_drawing/#lines')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_click_to_create_drawing/cursor')

  check_eq(#Editor_state.lines, 2, '#lines')
  check_eq(Editor_state.cursor1.line, 2, 'cursor')

  io.write('\ntest_backspace_to_delete_drawing')

  check_eq(#Editor_state.lines, 1, 'F - test_backspace_to_delete_drawing/#lines')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_backspace_to_delete_drawing/cursor')

  check_eq(#Editor_state.lines, 1, '#lines')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')

  io.write('\ntest_backspace_from_start_of_final_line')

  check_eq(#Editor_state.lines, 1, 'F - test_backspace_from_start_of_final_line/#lines')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_backspace_from_start_of_final_line/cursor')
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_backspace_from_start_of_final_line/screen_top')

  check_eq(#Editor_state.lines, 1, '#lines')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')

  io.write('\ntest_insert_first_character')

  App.screen.check(y, 'a', 'F - test_insert_first_character/screen:1')

  App.screen.check(y, 'a', 'screen:1')

  io.write('\ntest_press_ctrl')

  io.write('\ntest_move_left')

  check_eq(Editor_state.cursor1.pos, 1, 'F - test_move_left')

  check_eq(Editor_state.cursor1.pos, 1, 'check')

  io.write('\ntest_move_right')

  check_eq(Editor_state.cursor1.pos, 2, 'F - test_move_right')

  check_eq(Editor_state.cursor1.pos, 2, 'check')

  io.write('\ntest_move_left_to_previous_line')

  check_eq(Editor_state.cursor1.line, 1, 'F - test_move_left_to_previous_line/line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_move_left_to_previous_line/pos')  -- past end of line

  check_eq(Editor_state.cursor1.line, 1, 'line')
  check_eq(Editor_state.cursor1.pos, 4, 'pos')  -- past end of line

  io.write('\ntest_move_right_to_next_line')

  check_eq(Editor_state.cursor1.line, 2, 'F - test_move_right_to_next_line/line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_move_right_to_next_line/pos')

  check_eq(Editor_state.cursor1.line, 2, 'line')
  check_eq(Editor_state.cursor1.pos, 1, 'pos')

  io.write('\ntest_move_to_start_of_word')

  check_eq(Editor_state.cursor1.pos, 1, 'F - test_move_to_start_of_word')

  check_eq(Editor_state.cursor1.pos, 1, 'check')

  io.write('\ntest_move_to_start_of_previous_word')

  check_eq(Editor_state.cursor1.pos, 1, 'F - test_move_to_start_of_previous_word')

  check_eq(Editor_state.cursor1.pos, 1, 'check')

  io.write('\ntest_skip_to_previous_word')

  check_eq(Editor_state.cursor1.pos, 1, 'F - test_skip_to_previous_word')

  check_eq(Editor_state.cursor1.pos, 1, 'check')

  io.write('\ntest_skip_past_tab_to_previous_word')

  check_eq(Editor_state.cursor1.pos, 9, 'F - test_skip_past_tab_to_previous_word')

  check_eq(Editor_state.cursor1.pos, 9, 'check')

  io.write('\ntest_skip_multiple_spaces_to_previous_word')

  check_eq(Editor_state.cursor1.pos, 1, 'F - test_skip_multiple_spaces_to_previous_word')

  check_eq(Editor_state.cursor1.pos, 1, 'check')

  io.write('\ntest_move_to_start_of_word_on_previous_line')

  check_eq(Editor_state.cursor1.line, 1, 'F - test_move_to_start_of_word_on_previous_line/line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_move_to_start_of_word_on_previous_line/pos')

  check_eq(Editor_state.cursor1.line, 1, 'line')
  check_eq(Editor_state.cursor1.pos, 5, 'pos')

  io.write('\ntest_move_past_end_of_word')

  check_eq(Editor_state.cursor1.pos, 4, 'F - test_move_past_end_of_word')

  check_eq(Editor_state.cursor1.pos, 4, 'check')

  io.write('\ntest_skip_to_next_word')

  check_eq(Editor_state.cursor1.pos, 8, 'F - test_skip_to_next_word')

  check_eq(Editor_state.cursor1.pos, 8, 'check')

  io.write('\ntest_skip_past_tab_to_next_word')

  check_eq(Editor_state.cursor1.pos, 4, 'F - test_skip_past_tab_to_next_word')

  check_eq(Editor_state.cursor1.pos, 4, 'check')

  io.write('\ntest_skip_multiple_spaces_to_next_word')

  check_eq(Editor_state.cursor1.pos, 9, 'F - test_skip_multiple_spaces_to_next_word')

  check_eq(Editor_state.cursor1.pos, 9, 'check')

  io.write('\ntest_move_past_end_of_word_on_next_line')

  check_eq(Editor_state.cursor1.line, 2, 'F - test_move_past_end_of_word_on_next_line/line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_move_past_end_of_word_on_next_line/pos')

  check_eq(Editor_state.cursor1.line, 2, 'line')
  check_eq(Editor_state.cursor1.pos, 4, 'pos')

  io.write('\ntest_click_moves_cursor')

  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_moves_cursor/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_click_moves_cursor/cursor:pos')

  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')

  check_nil(Editor_state.selection1.line, 'F - test_click_moves_cursor/selection:line')
  check_nil(Editor_state.selection1.pos, 'F - test_click_moves_cursor/selection:pos')

  check_nil(Editor_state.selection1.line, 'selection:line')
  check_nil(Editor_state.selection1.pos, 'selection:pos')

  io.write('\ntest_click_to_left_of_line')

  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_to_left_of_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_click_to_left_of_line/cursor:pos')
  check_nil(Editor_state.selection1.line, 'F - test_click_to_left_of_line/selection is empty to avoid perturbing future edits')

  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  check_nil(Editor_state.selection1.line, 'selection is empty to avoid perturbing future edits')

  io.write('\ntest_click_takes_margins_into_account')

  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_takes_margins_into_account/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_click_takes_margins_into_account/cursor:pos')
  check_nil(Editor_state.selection1.line, 'F - test_click_takes_margins_into_account/selection is empty to avoid perturbing future edits')

  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
  check_nil(Editor_state.selection1.line, 'selection is empty to avoid perturbing future edits')

  io.write('\ntest_click_on_empty_line')

  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_on_empty_line/cursor')

  check_eq(Editor_state.cursor1.line, 1, 'cursor')

  io.write('\ntest_draw_text')

  App.screen.check(y, 'abc', 'F - test_draw_text/screen:1')

  App.screen.check(y, 'abc', 'screen:1')

  App.screen.check(y, 'def', 'F - test_draw_text/screen:2')

  App.screen.check(y, 'def', 'screen:2')

  App.screen.check(y, 'ghi', 'F - test_draw_text/screen:3')

  App.screen.check(y, 'ghi', 'screen:3')

  io.write('\ntest_draw_wrapping_text')

  App.screen.check(y, 'abc', 'F - test_draw_wrapping_text/screen:1')

  App.screen.check(y, 'abc', 'screen:1')

  App.screen.check(y, 'de', 'F - test_draw_wrapping_text/screen:2')

  App.screen.check(y, 'de', 'screen:2')

  App.screen.check(y, 'fgh', 'F - test_draw_wrapping_text/screen:3')

  App.screen.check(y, 'fgh', 'screen:3')

  io.write('\ntest_draw_word_wrapping_text')

  App.screen.check(y, 'abc ', 'F - test_draw_word_wrapping_text/screen:1')

  App.screen.check(y, 'abc ', 'screen:1')

  App.screen.check(y, 'def ', 'F - test_draw_word_wrapping_text/screen:2')

  App.screen.check(y, 'def ', 'screen:2')

  App.screen.check(y, 'ghi', 'F - test_draw_word_wrapping_text/screen:3')

  App.screen.check(y, 'ghi', 'screen:3')

  io.write('\ntest_click_on_wrapping_line')

  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_on_wrapping_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_click_on_wrapping_line/cursor:pos')
  check_nil(Editor_state.selection1.line, 'F - test_click_on_wrapping_line/selection is empty to avoid perturbing future edits')

  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
  check_nil(Editor_state.selection1.line, 'selection is empty to avoid perturbing future edits')

  io.write('\ntest_click_on_wrapping_line_takes_margins_into_account')

  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_on_wrapping_line_takes_margins_into_account/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_click_on_wrapping_line_takes_margins_into_account/cursor:pos')
  check_nil(Editor_state.selection1.line, 'F - test_click_on_wrapping_line_takes_margins_into_account/selection is empty to avoid perturbing future edits')

  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
  check_nil(Editor_state.selection1.line, 'selection is empty to avoid perturbing future edits')

  io.write('\ntest_draw_text_wrapping_within_word')

  App.screen.check(y, 'abcd ', 'F - test_draw_text_wrapping_within_word/screen:1')

  App.screen.check(y, 'abcd ', 'screen:1')

  App.screen.check(y, 'e fgh', 'F - test_draw_text_wrapping_within_word/screen:2')

  App.screen.check(y, 'e fgh', 'screen:2')

  App.screen.check(y, 'ijk', 'F - test_draw_text_wrapping_within_word/screen:3')

  App.screen.check(y, 'ijk', 'screen:3')

  io.write('\ntest_draw_wrapping_text_containing_non_ascii')

  App.screen.check(y, 'mad', 'F - test_draw_wrapping_text_containing_non_ascii/screen:1')

  App.screen.check(y, 'mad', 'screen:1')

  App.screen.check(y, 'am I', 'F - test_draw_wrapping_text_containing_non_ascii/screen:2')

  App.screen.check(y, 'am I', 'screen:2')

  App.screen.check(y, '’m a', 'F - test_draw_wrapping_text_containing_non_ascii/screen:3')

  App.screen.check(y, '’m a', 'screen:3')

  io.write('\ntest_click_on_wrapping_line')

  App.screen.check(y, 'madam ', 'F - test_click_on_wrapping_line/baseline/screen:1')

  App.screen.check(y, 'madam ', 'baseline/screen:1')

  App.screen.check(y, "I'm ad", 'F - test_click_on_wrapping_line/baseline/screen:2')

  App.screen.check(y, "I'm ad", 'baseline/screen:2')

  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_on_wrapping_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 12, 'F - test_click_on_wrapping_line/cursor:pos')

  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 12, 'cursor:pos')

  io.write('\ntest_click_on_wrapping_line_rendered_from_partway_at_top_of_screen')

  App.screen.check(y, "I'm ad", 'F - test_click_on_wrapping_line_rendered_from_partway_at_top_of_screen/baseline/screen:2')

  App.screen.check(y, "I'm ad", 'baseline/screen:2')

  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_on_wrapping_line_rendered_from_partway_at_top_of_screen/cursor:line')
  check_eq(Editor_state.cursor1.pos, 12, 'F - test_click_on_wrapping_line_rendered_from_partway_at_top_of_screen/cursor:pos')

  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 12, 'cursor:pos')

  io.write('\ntest_click_past_end_of_wrapping_line')

  App.screen.check(y, 'madam ', 'F - test_click_past_end_of_wrapping_line/baseline/screen:1')

  App.screen.check(y, 'madam ', 'baseline/screen:1')

  App.screen.check(y, "I'm ad", 'F - test_click_past_end_of_wrapping_line/baseline/screen:2')

  App.screen.check(y, "I'm ad", 'baseline/screen:2')

  App.screen.check(y, 'am', 'F - test_click_past_end_of_wrapping_line/baseline/screen:3')

  App.screen.check(y, 'am', 'baseline/screen:3')

  check_eq(Editor_state.cursor1.pos, 15, 'F - test_click_past_end_of_wrapping_line/cursor')  -- one more than the number of UTF-8 code-points

  check_eq(Editor_state.cursor1.pos, 15, 'cursor')  -- one more than the number of UTF-8 code-points

  io.write('\ntest_click_past_end_of_wrapping_line_containing_non_ascii')

  App.screen.check(y, 'madam ', 'F - test_click_past_end_of_wrapping_line_containing_non_ascii/baseline/screen:1')

  App.screen.check(y, 'madam ', 'baseline/screen:1')

  App.screen.check(y, 'I’m ad', 'F - test_click_past_end_of_wrapping_line_containing_non_ascii/baseline/screen:2')

  App.screen.check(y, 'I’m ad', 'baseline/screen:2')

  App.screen.check(y, 'am', 'F - test_click_past_end_of_wrapping_line_containing_non_ascii/baseline/screen:3')

  App.screen.check(y, 'am', 'baseline/screen:3')

  check_eq(Editor_state.cursor1.pos, 15, 'F - test_click_past_end_of_wrapping_line_containing_non_ascii/cursor')  -- one more than the number of UTF-8 code-points

  check_eq(Editor_state.cursor1.pos, 15, 'cursor')  -- one more than the number of UTF-8 code-points

  io.write('\ntest_click_past_end_of_word_wrapping_line')

  App.screen.check(y, 'the quick brown fox ', 'F - test_click_past_end_of_word_wrapping_line/baseline/screen:1')

  App.screen.check(y, 'the quick brown fox ', 'baseline/screen:1')

  check_eq(Editor_state.cursor1.pos, 20, 'F - test_click_past_end_of_word_wrapping_line/cursor')

  check_eq(Editor_state.cursor1.pos, 20, 'cursor')

  io.write('\ntest_select_text')

  check_eq(Editor_state.selection1.line, 1, 'F - test_select_text/selection:line')
  check_eq(Editor_state.selection1.pos, 1, 'F - test_select_text/selection:pos')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_select_text/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_select_text/cursor:pos')

  check_eq(Editor_state.selection1.line, 1, 'selection:line')
  check_eq(Editor_state.selection1.pos, 1, 'selection:pos')
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')

  io.write('\ntest_cursor_movement_without_shift_resets_selection')

  check_nil(Editor_state.selection1.line, 'F - test_cursor_movement_without_shift_resets_selection')
  check_eq(Editor_state.lines[1].data, 'abc', 'F - test_cursor_movement_without_shift_resets_selection/data')

  check_nil(Editor_state.selection1.line, 'check')
  check_eq(Editor_state.lines[1].data, 'abc', 'data')

  io.write('\ntest_edit_deletes_selection')

  check_eq(Editor_state.lines[1].data, 'xbc', 'F - test_edit_deletes_selection')

  check_eq(Editor_state.lines[1].data, 'xbc', 'check')

  io.write('\ntest_edit_with_shift_key_deletes_selection')

  check_nil(Editor_state.selection1.line, 'F - test_edit_with_shift_key_deletes_selection')
  check_eq(Editor_state.lines[1].data, 'Dbc', 'F - test_edit_with_shift_key_deletes_selection/data')

  check_nil(Editor_state.selection1.line, 'check')
  check_eq(Editor_state.lines[1].data, 'Dbc', 'data')

  io.write('\ntest_copy_does_not_reset_selection')

  check_eq(App.clipboard, 'a', 'F - test_copy_does_not_reset_selection/clipboard')

  check_eq(App.clipboard, 'a', 'clipboard')

  check(Editor_state.selection1.line, 'F - test_copy_does_not_reset_selection')

  check(Editor_state.selection1.line, 'check')

  io.write('\ntest_cut')

  check_eq(App.clipboard, 'a', 'F - test_cut/clipboard')

  check_eq(App.clipboard, 'a', 'clipboard')

  check_eq(Editor_state.lines[1].data, 'bc', 'F - test_cut/data')

  check_eq(Editor_state.lines[1].data, 'bc', 'data')

  io.write('\ntest_paste_replaces_selection')

  check_eq(Editor_state.lines[1].data, 'xyzdef', 'F - test_paste_replaces_selection')

  check_eq(Editor_state.lines[1].data, 'xyzdef', 'check')

  io.write('\ntest_deleting_selection_may_scroll')

  App.screen.check(y, 'def', 'F - test_deleting_selection_may_scroll/baseline/screen:1')

  App.screen.check(y, 'def', 'baseline/screen:1')

  App.screen.check(y, 'ghi', 'F - test_deleting_selection_may_scroll/baseline/screen:2')

  App.screen.check(y, 'ghi', 'baseline/screen:2')

  App.screen.check(y, 'jkl', 'F - test_deleting_selection_may_scroll/baseline/screen:3')

  App.screen.check(y, 'jkl', 'baseline/screen:3')

  check_eq(Editor_state.screen_top1.line, 1, 'F - test_deleting_selection_may_scroll')
  check_eq(Editor_state.lines[1].data, 'ahi', 'F - test_deleting_selection_may_scroll/data')

  check_eq(Editor_state.screen_top1.line, 1, 'check')
  check_eq(Editor_state.lines[1].data, 'ahi', 'data')

  io.write('\ntest_edit_wrapping_text')

  App.screen.check(y, 'abc', 'F - test_edit_wrapping_text/screen:1')

  App.screen.check(y, 'abc', 'screen:1')

  App.screen.check(y, 'de', 'F - test_edit_wrapping_text/screen:2')

  App.screen.check(y, 'de', 'screen:2')

  App.screen.check(y, 'fg', 'F - test_edit_wrapping_text/screen:3')

  App.screen.check(y, 'fg', 'screen:3')

  io.write('\ntest_insert_newline')

  App.screen.check(y, 'abc', 'F - test_insert_newline/baseline/screen:1')

  App.screen.check(y, 'abc', 'baseline/screen:1')

  App.screen.check(y, 'def', 'F - test_insert_newline/baseline/screen:2')

  App.screen.check(y, 'def', 'baseline/screen:2')

  App.screen.check(y, 'ghi', 'F - test_insert_newline/baseline/screen:3')

  App.screen.check(y, 'ghi', 'baseline/screen:3')

  check_eq(Editor_state.screen_top1.line, 1, 'F - test_insert_newline/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_insert_newline/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_insert_newline/cursor:pos')

  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')

  App.screen.check(y, 'a', 'F - test_insert_newline/screen:1')

  App.screen.check(y, 'a', 'screen:1')

  App.screen.check(y, 'bc', 'F - test_insert_newline/screen:2')

  App.screen.check(y, 'bc', 'screen:2')

  App.screen.check(y, 'def', 'F - test_insert_newline/screen:3')

  App.screen.check(y, 'def', 'screen:3')

  io.write('\ntest_insert_newline_at_start_of_line')

  check_eq(Editor_state.cursor1.line, 2, 'F - test_insert_newline_at_start_of_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_insert_newline_at_start_of_line/cursor:pos')
  check_eq(Editor_state.lines[1].data, '', 'F - test_insert_newline_at_start_of_line/data:1')
  check_eq(Editor_state.lines[2].data, 'abc', 'F - test_insert_newline_at_start_of_line/data:2')

  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'cursor:pos')
  check_eq(Editor_state.lines[1].data, '', 'data:1')
  check_eq(Editor_state.lines[2].data, 'abc', 'data:2')

  io.write('\ntest_insert_from_clipboard')

  App.screen.check(y, 'abc', 'F - test_insert_from_clipboard/baseline/screen:1')

  App.screen.check(y, 'abc', 'baseline/screen:1')

  App.screen.check(y, 'def', 'F - test_insert_from_clipboard/baseline/screen:2')

  App.screen.check(y, 'def', 'baseline/screen:2')

  App.screen.check(y, 'ghi', 'F - test_insert_from_clipboard/baseline/screen:3')

  App.screen.check(y, 'ghi', 'baseline/screen:3')

  check_eq(Editor_state.screen_top1.line, 1, 'F - test_insert_from_clipboard/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_insert_from_clipboard/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_insert_from_clipboard/cursor:pos')

  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')

  App.screen.check(y, 'axy', 'F - test_insert_from_clipboard/screen:1')

  App.screen.check(y, 'axy', 'screen:1')

  App.screen.check(y, 'zbc', 'F - test_insert_from_clipboard/screen:2')

  App.screen.check(y, 'zbc', 'screen:2')

  App.screen.check(y, 'def', 'F - test_insert_from_clipboard/screen:3')

  App.screen.check(y, 'def', 'screen:3')

  io.write('\ntest_select_text_using_mouse')

  check_eq(Editor_state.selection1.line, 1, 'F - test_select_text_using_mouse/selection:line')
  check_eq(Editor_state.selection1.pos, 2, 'F - test_select_text_using_mouse/selection:pos')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_select_text_using_mouse/cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_select_text_using_mouse/cursor:pos')

  check_eq(Editor_state.selection1.line, 1, 'selection:line')
  check_eq(Editor_state.selection1.pos, 2, 'selection:pos')
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'cursor:pos')

  io.write('\ntest_select_text_using_mouse_and_shift')

  check_eq(Editor_state.selection1.line, 1, 'F - test_select_text_using_mouse_and_shift/selection:line')
  check_eq(Editor_state.selection1.pos, 2, 'F - test_select_text_using_mouse_and_shift/selection:pos')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_select_text_using_mouse_and_shift/cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_select_text_using_mouse_and_shift/cursor:pos')

  check_eq(Editor_state.selection1.line, 1, 'selection:line')
  check_eq(Editor_state.selection1.pos, 2, 'selection:pos')
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'cursor:pos')

  io.write('\ntest_select_text_repeatedly_using_mouse_and_shift')

  check_eq(Editor_state.selection1.line, 1, 'F - test_select_text_repeatedly_using_mouse_and_shift/selection:line')
  check_eq(Editor_state.selection1.pos, 2, 'F - test_select_text_repeatedly_using_mouse_and_shift/selection:pos')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_select_text_repeatedly_using_mouse_and_shift/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_select_text_repeatedly_using_mouse_and_shift/cursor:pos')

  check_eq(Editor_state.selection1.line, 1, 'selection:line')
  check_eq(Editor_state.selection1.pos, 2, 'selection:pos')
  check_eq(Editor_state.cursor1.line, 2, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')

  io.write('\ntest_cut_without_selection')

  check_nil(Editor_state.selection1.line, 'F - test_cut_without_selection')

  check_nil(Editor_state.selection1.line, 'check')

  io.write('\ntest_pagedown')

  App.screen.check(y, 'abc', 'F - test_pagedown/baseline/screen:1')

  App.screen.check(y, 'abc', 'baseline/screen:1')

  App.screen.check(y, 'def', 'F - test_pagedown/baseline/screen:2')

  App.screen.check(y, 'def', 'baseline/screen:2')

  check_eq(Editor_state.screen_top1.line, 2, 'F - test_pagedown/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_pagedown/cursor')

  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'cursor')

  App.screen.check(y, 'def', 'F - test_pagedown/screen:1')

  App.screen.check(y, 'def', 'screen:1')

  App.screen.check(y, 'ghi', 'F - test_pagedown/screen:2')

  App.screen.check(y, 'ghi', 'screen:2')

  io.write('\ntest_pagedown_skips_drawings')

  check_eq(Editor_state.lines[2].mode, 'drawing', 'F - test_pagedown_skips_drawings/baseline/lines')

  check_eq(Editor_state.lines[2].mode, 'drawing', 'baseline/lines')

  App.screen.check(y, 'abc', 'F - test_pagedown_skips_drawings/baseline/screen:1')

  App.screen.check(y, 'abc', 'baseline/screen:1')

  check_eq(Editor_state.screen_top1.line, 2, 'F - test_pagedown_skips_drawings/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_pagedown_skips_drawings/cursor')

  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'cursor')

  App.screen.check(y, 'def', 'F - test_pagedown_skips_drawings/screen:1')

  App.screen.check(y, 'def', 'screen:1')

  io.write('\ntest_pagedown_can_start_from_middle_of_long_wrapping_line')

  App.screen.check(y, 'abc ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/baseline/screen:1')

  App.screen.check(y, 'abc ', 'baseline/screen:1')

  App.screen.check(y, 'def ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/baseline/screen:2')

  App.screen.check(y, 'def ', 'baseline/screen:2')

  App.screen.check(y, 'ghi ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/baseline/screen:3')

  App.screen.check(y, 'ghi ', 'baseline/screen:3')

  check_eq(Editor_state.screen_top1.line, 1, 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 9, 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen_top:pos')

  check_eq(Editor_state.screen_top1.line, 1, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 9, 'screen_top:pos')

  App.screen.check(y, 'ghi ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen:1')

  App.screen.check(y, 'ghi ', 'screen:1')

  App.screen.check(y, 'jkl ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen:2')

  App.screen.check(y, 'jkl ', 'screen:2')

  App.screen.check(y, 'mno ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen:3')

  App.screen.check(y, 'mno ', 'screen:3')

  io.write('\ntest_pagedown_never_moves_up')

  check_eq(Editor_state.screen_top1.line, 1, 'F - test_pagedown_never_moves_up/screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 9, 'F - test_pagedown_never_moves_up/screen_top:pos')

  check_eq(Editor_state.screen_top1.line, 1, 'screen_top:line')
  check_eq(Editor_state.screen_top1.pos, 9, 'screen_top:pos')

  io.write('\ntest_down_arrow_moves_cursor')

  App.screen.check(y, 'abc', 'F - test_down_arrow_moves_cursor/baseline/screen:1')

  App.screen.check(y, 'abc', 'baseline/screen:1')

  App.screen.check(y, 'def', 'F - test_down_arrow_moves_cursor/baseline/screen:2')

  App.screen.check(y, 'def', 'baseline/screen:2')

  App.screen.check(y, 'ghi', 'F - test_down_arrow_moves_cursor/baseline/screen:3')

  App.screen.check(y, 'ghi', 'baseline/screen:3')

  check_eq(Editor_state.screen_top1.line, 1, 'F - test_down_arrow_moves_cursor/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_down_arrow_moves_cursor/cursor')

  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'cursor')

  App.screen.check(y, 'abc', 'F - test_down_arrow_moves_cursor/screen:1')

  App.screen.check(y, 'abc', 'screen:1')

  App.screen.check(y, 'def', 'F - test_down_arrow_moves_cursor/screen:2')

  App.screen.check(y, 'def', 'screen:2')

  App.screen.check(y, 'ghi', 'F - test_down_arrow_moves_cursor/screen:3')

  App.screen.check(y, 'ghi', 'screen:3')

  io.write('\ntest_down_arrow_scrolls_down_by_one_line')

  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:1')

  App.screen.check(y, 'abc', 'baseline/screen:1')

  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:2')

  App.screen.check(y, 'def', 'baseline/screen:2')

  App.screen.check(y, 'ghi', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:3')

  App.screen.check(y, 'ghi', 'baseline/screen:3')

  check_eq(Editor_state.screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_line/screen_top')
  check_eq(Editor_state.cursor1.line, 4, 'F - test_down_arrow_scrolls_down_by_one_line/cursor')

  check_eq(Editor_state.screen_top1.line, 2, 'screen_top')
  check_eq(Editor_state.cursor1.line, 4, 'cursor')