-- undo/redo by managing the sequence of events in the current session
-- based on https://github.com/akkartik/mu1/blob/master/edit/012-editor-undo.mu
-- Incredibly inefficient; we make a copy of lines on every single keystroke.
-- The hope here is that we're either editing small files or just reading large files.
-- TODO: highlight stuff inserted by any undo/redo operation
-- TODO: coalesce multiple similar operations
  end
end
    return result
  end
end
    return result
  end
end
-- Make copies of objects; the rest of the app may mutate them in place, but undo requires immutable histories.
  -- compare with App.initialize_globals
  local event = {
    lines={},
    -- no filename; undo history is cleared when filename changes
  }
  -- deep copy lines without cached stuff like text fragments
  end
  return event
end
-- https://stackoverflow.com/questions/640642/how-do-you-copy-a-lua-table-by-value/26367080#26367080
function deepcopy(obj, seen)
  if type(obj) ~= 'table' then return obj end
  if seen and seen[obj] then return seen[obj] end
  local s = seen or {}
  local result = setmetatable({}, getmetatable(obj))
  s[obj] = result
  for k,v in pairs(obj) do
    result[deepcopy(k, s)] = deepcopy(v, s)
  end
  return result
end
function minmax(a, b)
  return math.min(a,b), math.max(a,b)
end
function patch(lines, from, to)
--?   if #from.lines == 1 and #to.lines == 1 then
--?     assert(from.start_line == from.end_line)
--?     assert(to.start_line == to.end_line)
--?     assert(from.start_line == to.start_line)
--?     lines[from.start_line] = to.lines[1]
--?     return
--?   end
  assert(from.start_line == to.start_line)
  for i=from.end_line,from.start_line,-1 do
    table.remove(lines, i)
  end
  assert(#to.lines == to.end_line-to.start_line+1)
  for i=1,#to.lines do
    table.insert(lines, to.start_line+i-1, to.lines[i])
  end
end
function patch_placeholders(line_cache, from, to)
  assert(from.start_line == to.start_line)
  for i=from.end_line,from.start_line,-1 do
    table.remove(line_cache, i)
  end
  assert(#to.lines == to.end_line-to.start_line+1)
  for i=1,#to.lines do
    table.insert(line_cache, to.start_line+i-1, {})
  end
end
  for i=s,e do
    local line = State.lines[i]
    table.insert(event.lines, {data=line.data, dataB=line.dataB})
    start_line=s,
    end_line=e,
    screen_top=deepcopy(State.screen_top1),
    selection=deepcopy(State.selection1),
    cursor=deepcopy(State.cursor1),
  -- Snapshot everything by default, but subset if requested.
    e = s
  end
  if s < 1 then s = 1 end
  if e < 1 then e = 1 end
  if e > #State.lines then e = #State.lines end
  if s > #State.lines then s = #State.lines end
  assert(#State.lines > 0)
  assert(s)
  if e == nil then
function snapshot(State, s,e)
-- Copy all relevant global state.
function redo_event(State)
  if State.next_history <= #State.history then
--?     print('restoring history', State.next_history+1)
    local result = State.history[State.next_history]
    State.next_history = State.next_history+1
function undo_event(State)
  if State.next_history > 1 then
--?     print('moving to history', State.next_history-1)
    State.next_history = State.next_history-1
    local result = State.history[State.next_history]
function record_undo_event(State, data)
  State.history[State.next_history] = data
  State.next_history = State.next_history+1
  for i=State.next_history,#State.history do
    State.history[i] = nil

-- major tests for text editing flows
function test_insert_first_character()
  io.write('\ntest_insert_first_character')
  App.screen.init{width=120, height=60}
  App.screen.check(y, 'a', 'F - test_insert_first_character/screen:1')
end
function test_move_left_to_previous_line()
  io.write('\ntest_move_left_to_previous_line')
  App.screen.init{width=120, height=60}
  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
end
function test_move_right_to_next_line()
  io.write('\ntest_move_right_to_next_line')
  App.screen.init{width=120, height=60}
  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')
end
function test_move_to_start_of_word()
  io.write('\ntest_move_to_start_of_word')
  App.screen.init{width=120, height=60}
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_move_to_start_of_word')
end
function test_move_to_start_of_previous_word()
  io.write('\ntest_move_to_start_of_previous_word')
  App.screen.init{width=120, height=60}
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_move_to_start_of_previous_word')
end
function test_skip_to_previous_word()
  io.write('\ntest_skip_to_previous_word')
  App.screen.init{width=120, height=60}
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_skip_to_previous_word')
end
function test_skip_past_tab_to_previous_word()
  io.write('\ntest_skip_past_tab_to_previous_word')
  App.screen.init{width=120, height=60}
  check_eq(Editor_state.cursor1.pos, 9, 'F - test_skip_past_tab_to_previous_word')
end
function test_skip_multiple_spaces_to_previous_word()
  io.write('\ntest_skip_multiple_spaces_to_previous_word')
  App.screen.init{width=120, height=60}
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_skip_multiple_spaces_to_previous_word')
end
function test_move_to_start_of_word_on_previous_line()
  io.write('\ntest_move_to_start_of_word_on_previous_line')
  App.screen.init{width=120, height=60}
  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')
end
function test_move_past_end_of_word()
  io.write('\ntest_move_past_end_of_word')
  App.screen.init{width=120, height=60}
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_move_past_end_of_word')
end
function test_skip_to_next_word()
  io.write('\ntest_skip_to_next_word')
  App.screen.init{width=120, height=60}
  check_eq(Editor_state.cursor1.pos, 8, 'F - test_skip_to_next_word')
end
function test_move_past_end_of_word_on_next_line()
  io.write('\ntest_move_past_end_of_word_on_next_line')
  App.screen.init{width=120, height=60}
  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')
end
  Editor_state.lines = load_array{'abc def', 'ghi'}
  Editor_state.cursor1 = {line=1, pos=8}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-right')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
function test_skip_past_tab_to_next_word()
  io.write('\ntest_skip_past_tab_to_next_word')
  App.screen.init{width=120, height=60}
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_skip_past_tab_to_next_word')
end
function test_skip_multiple_spaces_to_next_word()
  io.write('\ntest_skip_multiple_spaces_to_next_word')
  App.screen.init{width=120, height=60}
  check_eq(Editor_state.cursor1.pos, 9, 'F - test_skip_multiple_spaces_to_next_word')
end
  Editor_state.lines = load_array{'abc  def'}
  Editor_state.cursor1 = {line=1, pos=4}  -- at the start of second word
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-right')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc\tdef'}
  Editor_state.cursor1 = {line=1, pos=1}  -- at the space between words
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-right')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Editor_state.cursor1 = {line=1, pos=4}  -- at the space between words
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-right')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Editor_state.cursor1 = {line=1, pos=1}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-right')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def', 'ghi'}
  Editor_state.cursor1 = {line=2, pos=1}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc  def'}
  Editor_state.cursor1 = {line=1, pos=6}  -- at the start of second word
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def\tghi'}
  Editor_state.cursor1 = {line=1, pos=10}  -- within third word
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Editor_state.cursor1 = {line=1, pos=5}  -- at the start of second word
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Editor_state.cursor1 = {line=1, pos=4}  -- at the space between words
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc'}
  Editor_state.cursor1 = {line=1, pos=3}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'M-left')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def'}
  Editor_state.cursor1 = {line=1, pos=4}  -- past end of line
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'right')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def'}
  Editor_state.cursor1 = {line=2, pos=1}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'left')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
function test_draw_text()
  io.write('\ntest_draw_text')
  App.screen.init{width=120, height=60}
  App.screen.check(y, 'abc', 'F - test_draw_text/screen:1')
  App.screen.check(y, 'def', 'F - test_draw_text/screen:2')
  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}
  App.screen.check(y, 'abc', 'F - test_draw_wrapping_text/screen:1')
  y = y + Editor_state.line_height
end
function test_draw_word_wrapping_text()
  io.write('\ntest_draw_word_wrapping_text')
  App.screen.init{width=60, height=60}
  App.screen.check(y, 'abc ', 'F - test_draw_word_wrapping_text/screen:1')
  App.screen.check(y, 'def ', 'F - test_draw_word_wrapping_text/screen:2')
  App.screen.check(y, 'ghi', 'F - test_draw_word_wrapping_text/screen:3')
end
function test_click_with_mouse_on_wrapping_line_takes_margins_into_account()
  io.write('\ntest_click_with_mouse_on_wrapping_line_takes_margins_into_account')
  -- display two lines with cursor on one of them
  App.screen.init{width=100, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.left = 50  -- occupy only right side of screen
  Editor_state.lines = load_array{'abc def ghi jkl mno pqr stu'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=20}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- click on the other line
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  -- cursor moves
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse_on_wrapping_line_takes_margins_into_account/cursor:line')
end
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_click_with_mouse_on_wrapping_line_takes_margins_into_account/cursor:pos')
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}
  App.screen.check(y, 'abcd ', 'F - test_draw_text_wrapping_within_word/screen:1')
  y = y + Editor_state.line_height
end
function test_draw_wrapping_text_containing_non_ascii()
  -- draw a long line containing non-ASCII
  io.write('\ntest_draw_wrapping_text_containing_non_ascii')
  App.screen.init{width=60, height=60}
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
end
function test_edit_wrapping_text()
  io.write('\ntest_edit_wrapping_text')
  App.screen.init{width=50, height=60}
  App.screen.check(y, 'abc', 'F - test_edit_wrapping_text/screen:1')
  y = y + Editor_state.line_height
end
function test_insert_newline()
  io.write('\ntest_insert_newline')
  App.screen.check(y, 'abc', 'F - test_insert_newline/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_insert_newline/baseline/screen:2')
  App.screen.check(y, 'ghi', 'F - test_insert_newline/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')
  App.screen.check(y, 'a', 'F - test_insert_newline/screen:1')
  App.screen.check(y, 'bc', 'F - test_insert_newline/screen:2')
  App.screen.check(y, 'def', 'F - test_insert_newline/screen:3')
end
function test_insert_from_clipboard()
  io.write('\ntest_insert_from_clipboard')
  App.screen.check(y, 'abc', 'F - test_insert_from_clipboard/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_insert_from_clipboard/baseline/screen:2')
  App.screen.check(y, 'ghi', 'F - test_insert_from_clipboard/baseline/screen:3')
  App.clipboard = 'xy\nz'
  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')
  y = Editor_state.top
  App.screen.check(y, 'axy', 'F - test_insert_from_clipboard/screen:1')
  App.screen.check(y, 'zbc', 'F - test_insert_from_clipboard/screen:2')
  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}
end
function test_pagedown()
  io.write('\ntest_pagedown')
  App.screen.init{width=120, height=45}
  -- initially the first two lines are displayed
  App.screen.check(y, 'abc', 'F - test_pagedown/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_pagedown/baseline/screen:2')
  -- after pagedown the bottom line becomes the top
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_pagedown/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_pagedown/cursor')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_pagedown/screen:1')
  App.screen.check(y, 'ghi', 'F - test_pagedown/screen:2')
end
end
function test_down_arrow_moves_cursor()
  io.write('\ntest_down_arrow_moves_cursor')
  App.screen.init{width=120, height=60}
  -- initially the first three lines are displayed
  App.screen.check(y, 'abc', 'F - test_down_arrow_moves_cursor/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_down_arrow_moves_cursor/baseline/screen:2')
  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
  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')
  -- the screen is unchanged
  App.screen.check(y, 'abc', 'F - test_down_arrow_moves_cursor/screen:1')
  App.screen.check(y, 'def', 'F - test_down_arrow_moves_cursor/screen:2')
  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}
  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_line/baseline/screen:2')
  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
  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')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_line/screen:1')
  App.screen.check(y, 'ghi', 'F - test_down_arrow_scrolls_down_by_one_line/screen:2')
  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
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_screen_line/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line/baseline/screen:2')
  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
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_down_arrow_scrolls_down_by_one_screen_line/cursor:line')
  y = Editor_state.top
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_down_arrow_scrolls_down_by_one_screen_line/cursor:pos')
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen:1')
  App.screen.check(y, 'ghi ', 'F - test_down_arrow_scrolls_down_by_one_screen_line/screen:2')
  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
  Editor_state.lines = load_array{'abc', 'def', 'ghijkl', 'mno'}
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.check(y, 'abc', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:2')
  -- after hitting the down arrow the screen scrolls down by one line
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/cursor:line')
  y = Editor_state.top
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/cursor:pos')
  App.screen.check(y, 'def', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:1')
  y = y + Editor_state.line_height
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')
  Editor_state.lines = load_array{'abc', 'def', 'ghijkl', 'mno'}
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.check(y, 'abc', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:2')
  -- after hitting pagedown the screen scrolls down to start of a long line
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline2/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline2/cursor:line')
  check_eq(Editor_state.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
  y = y + Editor_state.line_height
  y = y + Editor_state.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}
  App.screen.check(y, 'abc', 'F - test_up_arrow_moves_cursor/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_up_arrow_moves_cursor/baseline/screen:2')
  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
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_up_arrow_moves_cursor/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_up_arrow_moves_cursor/cursor')
  -- the screen is unchanged
  App.screen.check(y, 'abc', 'F - test_up_arrow_moves_cursor/screen:1')
  App.screen.check(y, 'def', 'F - test_up_arrow_moves_cursor/screen:2')
  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}
  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_by_one_line/baseline/screen:1')
  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_by_one_line/baseline/screen:2')
  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
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_by_one_line/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_up_arrow_scrolls_up_by_one_line/cursor')
  y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_by_one_line/screen:1')
  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_by_one_line/screen:2')
  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
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Editor_state.cursor1 = {line=3, pos=6}
  Editor_state.screen_top1 = {line=3, pos=5}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_by_one_screen_line/baseline/screen:1')
  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.screen.check(y, 'ghi ', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:1')
  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:2')
  App.screen.check(y, 'mno', 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen:3')
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
  Editor_state.lines = load_array{'abc def', 'ghi', 'jkl', 'mno'}
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:1')
  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:2')
  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.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:1')
  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:2')
  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:3')
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}
  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_to_empty_line/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_empty_line/baseline/screen:2')
  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
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_to_empty_line/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_up_arrow_scrolls_up_to_empty_line/cursor')
  y = Editor_state.top
  -- empty first line
  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_to_empty_line/screen:2')
  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}
  -- initially the last two lines are displayed
  App.screen.check(y, 'def', 'F - test_pageup/baseline/screen:1')
  App.screen.check(y, 'ghi', 'F - test_pageup/baseline/screen:2')
  -- after pageup the cursor goes to first line
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_pageup/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_pageup/cursor')
  y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_pageup/screen:1')
  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
  Editor_state.lines = load_array{'abc def', 'ghi', 'jkl', 'mno'}
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.check(y, 'ghi', 'F - test_pageup_scrolls_up_by_screen_line/baseline/screen:1')
  App.screen.check(y, 'jkl', 'F - test_pageup_scrolls_up_by_screen_line/baseline/screen:2')
  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
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_pageup_scrolls_up_by_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_pageup_scrolls_up_by_screen_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_pageup_scrolls_up_by_screen_line/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'abc ', 'F - test_pageup_scrolls_up_by_screen_line/screen:1')
  App.screen.check(y, 'def', 'F - test_pageup_scrolls_up_by_screen_line/screen:2')
  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')
  App.screen.check(y, 'jkl', 'F - test_pageup_scrolls_up_from_middle_screen_line/baseline/screen:2')
  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
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_pageup_scrolls_up_from_middle_screen_line/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'abc ', 'F - test_pageup_scrolls_up_from_middle_screen_line/screen:1')
  App.screen.check(y, 'def', 'F - test_pageup_scrolls_up_from_middle_screen_line/screen:2')
  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
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Editor_state.cursor1 = {line=3, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.check(y, 'abc', 'F - test_enter_on_bottom_line_scrolls_down/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_enter_on_bottom_line_scrolls_down/baseline/screen:2')
  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
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_enter_on_bottom_line_scrolls_down/screen_top')
  check_eq(Editor_state.cursor1.line, 4, 'F - test_enter_on_bottom_line_scrolls_down/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_enter_on_bottom_line_scrolls_down/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_enter_on_bottom_line_scrolls_down/screen:1')
  App.screen.check(y, 'g', 'F - test_enter_on_bottom_line_scrolls_down/screen:2')
  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
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Editor_state.cursor1 = {line=4, pos=2}
  Editor_state.screen_top1 = {line=4, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  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
  check_eq(Editor_state.screen_top1.line, 4, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen_top')
  check_eq(Editor_state.cursor1.line, 5, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'j', 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen:1')
  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.check(y, 'abc def ghi ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline1/screen:1')
  App.screen.check(y, 'jkl mno pqr ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline1/screen:2')
  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.screen.check(y, 'abc def ghi ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline2/screen:1')
  App.screen.check(y, 'jkl mno pqr ', 'F - test_position_cursor_on_recently_edited_wrapping_line/baseline2/screen:2')
  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
  -- cursor should move
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}
  App.screen.check(y, 'def', 'F - test_backspace_can_scroll_up/baseline/screen:1')
  App.screen.check(y, 'ghi', 'F - test_backspace_can_scroll_up/baseline/screen:2')
  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up/baseline/screen:3')
  -- after hitting backspace the screen scrolls up by one line
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_backspace_can_scroll_up/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_backspace_can_scroll_up/cursor')
  y = Editor_state.top
  App.screen.check(y, 'abcdef', 'F - test_backspace_can_scroll_up/screen:1')
  App.screen.check(y, 'ghi', 'F - test_backspace_can_scroll_up/screen:2')
  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
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Editor_state.cursor1 = {line=3, pos=5}
  Editor_state.screen_top1 = {line=3, pos=5}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up_screen_line/baseline/screen:1')
  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
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno', 'F - test_backspace_can_scroll_up_screen_line/screen:3')
end
function test_backspace_past_line_boundary()
  io.write('\ntest_backspace_past_line_boundary')
  -- position cursor at start of a (non-first) line
  Editor_state.lines = load_array{'abc', 'def'}
  Editor_state.cursor1 = {line=2, pos=1}
  Text.redraw_all(Editor_state)
  -- backspace joins with previous line
end
function test_undo_insert_text()
  io.write('\ntest_undo_insert_text')
  App.screen.init{width=120, height=60}
  -- insert a character
  check_eq(Editor_state.cursor1.line, 2, 'F - test_undo_insert_text/baseline/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_undo_insert_text/baseline/cursor:pos')
  App.screen.check(y, 'abc', 'F - test_undo_insert_text/baseline/screen:1')
  App.screen.check(y, 'defg', 'F - test_undo_insert_text/baseline/screen:2')
  App.screen.check(y, 'xyz', 'F - test_undo_insert_text/baseline/screen:3')
  -- undo
  check_eq(Editor_state.cursor1.line, 2, 'F - test_undo_insert_text/cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_undo_insert_text/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_undo_insert_text/screen:1')
  App.screen.check(y, 'def', 'F - test_undo_insert_text/screen:2')
  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}
  -- delete a character
  check_eq(Editor_state.cursor1.line, 2, 'F - test_undo_delete_text/baseline/cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_undo_delete_text/baseline/cursor:pos')
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_undo_delete_text/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_undo_delete_text/baseline/screen:2')
  App.screen.check(y, 'xyz', 'F - test_undo_delete_text/baseline/screen:3')
  -- undo
--?   -- after undo, the backspaced key is selected
  check_eq(Editor_state.cursor1.line, 2, 'F - test_undo_delete_text/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_undo_delete_text/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'abc', 'F - test_undo_delete_text/screen:1')
  App.screen.check(y, 'defg', 'F - test_undo_delete_text/screen:2')
  App.screen.check(y, 'xyz', 'F - test_undo_delete_text/screen:3')
function test_search()
  io.write('\ntest_search')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  -- search for a string
  edit.run_after_keychord(Editor_state, 'C-f')
  edit.run_after_textinput(Editor_state, 'd')
  edit.run_after_keychord(Editor_state, 'return')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_search/1/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_search/1/cursor:pos')
  -- reset cursor
  Editor_state.cursor1 = {line=1, pos=1}
  -- search for second occurrence
  edit.run_after_keychord(Editor_state, 'C-f')
  edit.run_after_textinput(Editor_state, 'de')
  edit.run_after_keychord(Editor_state, 'down')
  edit.run_after_keychord(Editor_state, 'return')
  check_eq(Editor_state.cursor1.line, 4, 'F - test_search/2/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_search/2/cursor:pos')
end
function test_search_wrap()
  io.write('\ntest_search_wrap')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=3}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  -- search for a string
  edit.run_after_keychord(Editor_state, 'C-f')
  edit.run_after_textinput(Editor_state, 'a')
  edit.run_after_keychord(Editor_state, 'return')
  -- cursor wraps
  check_eq(Editor_state.cursor1.line, 1, 'F - test_search_wrap/1/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_search_wrap/1/cursor:pos')
end
function test_search_wrap_upwards()
  io.write('\ntest_search_wrap_upwards')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc abd'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  -- search upwards for a string
  edit.run_after_keychord(Editor_state, 'C-f')
  edit.run_after_textinput(Editor_state, 'a')
  edit.run_after_keychord(Editor_state, 'up')
  -- cursor wraps
  check_eq(Editor_state.cursor1.line, 1, 'F - test_search_wrap_upwards/1/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_search_wrap_upwards/1/cursor:pos')
end
function test_search_upwards()
  io.write('\ntest_search_upwards')
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc abd'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  -- search for a string
  edit.run_after_keychord(Editor_state, 'C-f')
  edit.run_after_textinput(Editor_state, 'a')
  -- search for previous occurrence
  edit.run_after_keychord(Editor_state, 'up')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_search_upwards/2/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_search_upwards/2/cursor:pos')
end
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'deg'}
end
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'C-z')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'backspace')
  Editor_state.lines = load_array{'abc', 'defg', 'xyz'}
  Editor_state.cursor1 = {line=2, pos=5}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'C-z')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  local y = Editor_state.top
  edit.draw(Editor_state)
  edit.run_after_textinput(Editor_state, 'g')
  Editor_state.lines = load_array{'abc', 'def', 'xyz'}
  Editor_state.cursor1 = {line=2, pos=4}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  edit.run_after_keychord(Editor_state, 'backspace')
  check_eq(Editor_state.lines[1].data, 'abcdef', "F - test_backspace_past_line_boundary")
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_backspace_can_scroll_up_screen_line/screen_top')
  check_eq(Editor_state.screen_top1.pos, 1, 'F - test_backspace_can_scroll_up_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_backspace_can_scroll_up_screen_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_backspace_can_scroll_up_screen_line/cursor:pos')
  App.screen.check(y, 'kl', 'F - test_backspace_can_scroll_up_screen_line/screen:2')
  edit.run_after_keychord(Editor_state, 'backspace')
  y = Editor_state.top
  App.screen.check(y, 'ghij', 'F - test_backspace_can_scroll_up_screen_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'backspace')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  check_eq(Editor_state.cursor1.line, 1, 'F - test_position_cursor_on_recently_edited_wrapping_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 26, 'F - test_position_cursor_on_recently_edited_wrapping_line/cursor:pos')
  edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+Editor_state.line_height*2+5, 1)
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  y = Editor_state.top
  edit.run_after_textinput(Editor_state, 's')
  edit.run_after_textinput(Editor_state, 't')
  edit.run_after_textinput(Editor_state, 'u')
  check_eq(Editor_state.cursor1.pos, 28, 'F - test_position_cursor_on_recently_edited_wrapping_line/cursor:pos')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  App.screen.init{width=100, height=200}
  Editor_state.lines = load_array{'abc def ghi jkl mno pqr ', 'xyz'}
  Editor_state.cursor1 = {line=1, pos=25}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
function test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom()
  io.write('\ntest_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom')
  -- display just an empty bottom line on screen
  Editor_state.lines = load_array{'abc', ''}
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  Text.redraw_all(Editor_state)
  -- after hitting the inserting_text key the screen does not scroll down
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen_top')
  check_eq(Editor_state.cursor1.line, 2, 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:pos')
  local y = Editor_state.top
  App.screen.check(y, 'a', 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen:1')
end
  edit.run_after_textinput(Editor_state, 'a')
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
function test_typing_on_bottom_line_scrolls_down()
  io.write('\ntest_typing_on_bottom_line_scrolls_down')
  -- display a few lines with cursor on bottom line
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Editor_state.cursor1 = {line=3, pos=4}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.check(y, 'abc', 'F - test_typing_on_bottom_line_scrolls_down/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_typing_on_bottom_line_scrolls_down/baseline/screen:2')
  App.screen.check(y, 'ghi', 'F - test_typing_on_bottom_line_scrolls_down/baseline/screen:3')
  -- after typing something the line wraps and the screen scrolls down
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_typing_on_bottom_line_scrolls_down/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_typing_on_bottom_line_scrolls_down/cursor:line')
  check_eq(Editor_state.cursor1.pos, 7, 'F - test_typing_on_bottom_line_scrolls_down/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_typing_on_bottom_line_scrolls_down/screen:1')
  y = y + Editor_state.line_height
end
function test_left_arrow_scrolls_up_in_wrapped_line()
  io.write('\ntest_left_arrow_scrolls_up_in_wrapped_line')
  -- display lines starting from second screen line of a line
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Editor_state.screen_top1 = {line=3, pos=5}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  -- cursor is at top of screen
  App.screen.check(y, 'jkl', 'F - test_left_arrow_scrolls_up_in_wrapped_line/baseline/screen:1')
  App.screen.check(y, 'mno', 'F - test_left_arrow_scrolls_up_in_wrapped_line/baseline/screen:2')
  -- after hitting the left arrow the screen scrolls up to first screen line
  App.screen.check(y, 'ghi ', 'F - test_left_arrow_scrolls_up_in_wrapped_line/screen:1')
  App.screen.check(y, 'jkl', 'F - test_left_arrow_scrolls_up_in_wrapped_line/screen:2')
  App.screen.check(y, 'mno', 'F - test_left_arrow_scrolls_up_in_wrapped_line/screen:3')
end
function test_right_arrow_scrolls_down_in_wrapped_line()
  io.write('\ntest_right_arrow_scrolls_down_in_wrapped_line')
  -- display the first three lines with the cursor on the bottom line
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  -- cursor is at bottom right of screen
  App.screen.check(y, 'abc', 'F - test_right_arrow_scrolls_down_in_wrapped_line/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_right_arrow_scrolls_down_in_wrapped_line/baseline/screen:2')
  App.screen.check(y, 'ghi ', 'F - test_right_arrow_scrolls_down_in_wrapped_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting the right arrow the screen scrolls down by one line
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_right_arrow_scrolls_down_in_wrapped_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_right_arrow_scrolls_down_in_wrapped_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 6, 'F - test_right_arrow_scrolls_down_in_wrapped_line/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_right_arrow_scrolls_down_in_wrapped_line/screen:1')
  App.screen.check(y, 'ghi ', 'F - test_right_arrow_scrolls_down_in_wrapped_line/screen:2')
  App.screen.check(y, 'jkl', 'F - test_right_arrow_scrolls_down_in_wrapped_line/screen:3')
end
function test_home_scrolls_up_in_wrapped_line()
  io.write('\ntest_home_scrolls_up_in_wrapped_line')
  -- display lines starting from second screen line of a line
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Editor_state.screen_top1 = {line=3, pos=5}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  -- cursor is at top of screen
  App.screen.check(y, 'jkl', 'F - test_home_scrolls_up_in_wrapped_line/baseline/screen:1')
  App.screen.check(y, 'mno', 'F - test_home_scrolls_up_in_wrapped_line/baseline/screen:2')
  -- after hitting home the screen scrolls up to first screen line
  App.screen.check(y, 'ghi ', 'F - test_home_scrolls_up_in_wrapped_line/screen:1')
  App.screen.check(y, 'jkl', 'F - test_home_scrolls_up_in_wrapped_line/screen:2')
  App.screen.check(y, 'mno', 'F - test_home_scrolls_up_in_wrapped_line/screen:3')
end
function test_end_scrolls_down_in_wrapped_line()
  io.write('\ntest_end_scrolls_down_in_wrapped_line')
  -- display the first three lines with the cursor on the bottom line
  Editor_state.lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  -- cursor is at bottom right of screen
  App.screen.check(y, 'abc', 'F - test_end_scrolls_down_in_wrapped_line/baseline/screen:1')
  App.screen.check(y, 'def', 'F - test_end_scrolls_down_in_wrapped_line/baseline/screen:2')
  App.screen.check(y, 'ghi ', 'F - test_end_scrolls_down_in_wrapped_line/baseline/screen:3')  -- line wrapping includes trailing whitespace
  -- after hitting end the screen scrolls down by one line
  check_eq(Editor_state.screen_top1.line, 2, 'F - test_end_scrolls_down_in_wrapped_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_end_scrolls_down_in_wrapped_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 8, 'F - test_end_scrolls_down_in_wrapped_line/cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'def', 'F - test_end_scrolls_down_in_wrapped_line/screen:1')
  App.screen.check(y, 'ghi ', 'F - test_end_scrolls_down_in_wrapped_line/screen:2')
  App.screen.check(y, 'jkl', 'F - test_end_scrolls_down_in_wrapped_line/screen:3')
end
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'end')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  Editor_state.cursor1 = {line=3, pos=5}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_home_scrolls_up_in_wrapped_line/screen_top')
  check_eq(Editor_state.screen_top1.pos, 1, 'F - test_home_scrolls_up_in_wrapped_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_home_scrolls_up_in_wrapped_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_home_scrolls_up_in_wrapped_line/cursor:pos')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'home')
  y = Editor_state.top
  y = y + Editor_state.line_height
  Editor_state.cursor1 = {line=3, pos=5}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'right')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  Editor_state.cursor1 = {line=3, pos=5}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_left_arrow_scrolls_up_in_wrapped_line/screen_top')
  check_eq(Editor_state.screen_top1.pos, 1, 'F - test_left_arrow_scrolls_up_in_wrapped_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_left_arrow_scrolls_up_in_wrapped_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'F - test_left_arrow_scrolls_up_in_wrapped_line/cursor:pos')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'left')
  y = Editor_state.top
  y = y + Editor_state.line_height
  Editor_state.cursor1 = {line=3, pos=5}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  App.screen.check(y, 'kl', 'F - test_typing_on_bottom_line_scrolls_down/screen:3')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghij', 'F - test_typing_on_bottom_line_scrolls_down/screen:2')
  edit.run_after_textinput(Editor_state, 'j')
  edit.run_after_textinput(Editor_state, 'k')
  edit.run_after_textinput(Editor_state, 'l')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'return')
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'return')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'pageup')
  y = y + Editor_state.line_height
  -- display a few lines starting from the middle of a line (Editor_state.cursor1.pos > 1)
  Editor_state.lines = load_array{'abc def', 'ghi jkl', 'mno'}
  Editor_state.cursor1 = {line=2, pos=5}
  Editor_state.screen_top1 = {line=2, pos=5}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'pageup')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'pageup')
  y = y + Editor_state.line_height
  edit.draw(Editor_state)
  local y = Editor_state.top
  Editor_state.lines = load_array{'abc', 'def', 'ghi'}
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'up')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  Editor_state.lines = load_array{'', 'abc', 'def', 'ghi', 'jkl'}
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  check_eq(Editor_state.screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen_top')
  check_eq(Editor_state.screen_top1.pos, 5, 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'F - test_up_arrow_scrolls_up_to_final_screen_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_up_arrow_scrolls_up_to_final_screen_line/cursor:pos')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'up')
  y = Editor_state.top
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen_top')
  check_eq(Editor_state.screen_top1.pos, 1, 'F - test_up_arrow_scrolls_up_by_one_screen_line/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_up_arrow_scrolls_up_by_one_screen_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_up_arrow_scrolls_up_by_one_screen_line/cursor:pos')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'up')
  y = Editor_state.top
  y = y + Editor_state.line_height
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'up')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  y = Editor_state.top
  edit.run_after_keychord(Editor_state, 'up')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  App.screen.check(y, 'kl', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen:2')
  check_eq(Editor_state.screen_top1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen_top')
  check_eq(Editor_state.cursor1.line, 3, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/cursor:line')
  y = Editor_state.top
  App.screen.check(y, 'ghij', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/screen:1')
  check_eq(Editor_state.cursor1.pos, 5, 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/cursor:pos')
  edit.run_after_keychord(Editor_state, 'down')
  edit.run_after_keychord(Editor_state, 'pagedown')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghij', 'F - test_page_down_followed_by_down_arrow_does_not_scroll_screen_up/baseline/screen:3')
  y = y + Editor_state.line_height
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  App.screen.check(y, 'kl', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:3')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghij', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/screen:2')
  edit.run_after_keychord(Editor_state, 'down')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghij', 'F - test_down_arrow_scrolls_down_by_one_screen_line_after_splitting_within_word/baseline/screen:3')
  y = y + Editor_state.line_height
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'down')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'down')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  y = Editor_state.top
  edit.run_after_keychord(Editor_state, 'down')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.draw(Editor_state)
  local y = Editor_state.top
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
function test_pagedown_never_moves_up()
  io.write('\ntest_pagedown_never_moves_up')
  -- draw the final screen line of a wrapping line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def ghi'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=9}
  Editor_state.screen_top1 = {line=1, pos=9}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  -- pagedown makes no change
  edit.run_after_keychord(Editor_state, 'pagedown')
  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')
end
function test_pagedown_can_start_from_middle_of_long_wrapping_line()
  io.write('\ntest_pagedown_can_start_from_middle_of_long_wrapping_line')
  -- draw a few lines starting from a very long wrapping line
  Editor_state.lines = load_array{'abc def ghi jkl mno pqr stu vwx yza bcd efg hij', 'XYZ'}
  Editor_state.cursor1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.check(y, 'abc ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/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, 'ghi ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/baseline/screen:3')
  -- after pagedown we scroll down the very long wrapping line
  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')
  y = Editor_state.top
  App.screen.check(y, 'ghi ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'mno ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen:3')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl ', 'F - test_pagedown_can_start_from_middle_of_long_wrapping_line/screen:2')
  edit.run_after_keychord(Editor_state, 'pagedown')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'pagedown')
  y = y + Editor_state.line_height
  edit.draw(Editor_state)
  local y = Editor_state.top
  Editor_state.lines = load_array{'abc', 'def', 'ghi'}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'xyz'}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  check_eq(Editor_state.cursor1.line, 1, 'F - test_move_cursor_using_mouse/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_move_cursor_using_mouse/cursor:pos')
  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
  edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  edit.run_after_keychord(Editor_state, 'C-v')
  -- paste some text including a newline, check that new line is created
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  -- display a few lines
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Editor_state.cursor1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
end
function test_insert_newline_at_start_of_line()
  io.write('\ntest_insert_newline_at_start_of_line')
  -- display a line
  Editor_state.lines = load_array{'abc'}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  -- hitting the enter key splits the 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')
  edit.run_after_keychord(Editor_state, 'return')
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  y = Editor_state.top
  -- hitting the enter key splits the line
  edit.run_after_keychord(Editor_state, 'return')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  -- display a few lines
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Editor_state.cursor1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  App.screen.check(y, 'fg', 'F - test_edit_wrapping_text/screen:3')
  y = y + Editor_state.line_height
  App.screen.check(y, 'de', 'F - test_edit_wrapping_text/screen:2')
  Editor_state.lines = load_array{'abc', 'def', 'xyz'}
  Editor_state.cursor1 = {line=2, pos=4}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  edit.run_after_textinput(Editor_state, 'g')
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
function test_click_on_wrapping_line()
  io.write('\ntest_click_on_wrapping_line')
  -- display a wrapping line
  Editor_state.lines = load_array{"madam I'm adam"}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  App.screen.check(y, 'madam ', 'F - test_click_on_wrapping_line/baseline/screen:1')
  y = y + Editor_state.line_height
  -- click past end of second screen line
  -- cursor moves to end of screen line
end
function test_click_past_end_of_wrapping_line()
  io.write('\ntest_click_past_end_of_wrapping_line')
  -- display a wrapping line
  Editor_state.lines = load_array{"madam I'm adam"}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  App.screen.check(y, 'madam ', 'F - test_click_past_end_of_wrapping_line/baseline/screen:1')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  -- click past the end of it
  -- cursor moves to end of line
end
  -- display a wrapping line containing non-ASCII
  Editor_state.lines = load_array{'madam I’m adam'}  -- notice the non-ASCII apostrophe
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  -- click past the end of it
  -- cursor moves to end of line
end
function test_click_past_end_of_word_wrapping_line()
  io.write('\ntest_click_past_end_of_word_wrapping_line')
  -- display a long line wrapping at a word boundary on a screen of more realistic length
  Editor_state.lines = load_array{'the quick brown fox jumped over the lazy dog'}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  App.screen.check(y, 'the quick brown fox ', 'F - test_click_past_end_of_word_wrapping_line/baseline/screen:1')
  -- cursor moves to end of screen line
end
  check_eq(Editor_state.cursor1.pos, 20, 'F - test_click_past_end_of_word_wrapping_line/cursor')
  -- click past the end of the screen line
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  y = y + Editor_state.line_height
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.init{width=160, height=80}
  Editor_state = edit.initialize_test_state()
                                -- 0        1         2
                                -- 123456789012345678901
  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
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  App.screen.check(y, 'am', 'F - test_click_past_end_of_wrapping_line_containing_non_ascii/baseline/screen:3')
  App.screen.check(y, 'I’m ad', 'F - test_click_past_end_of_wrapping_line_containing_non_ascii/baseline/screen:2')
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'madam ', 'F - test_click_past_end_of_wrapping_line_containing_non_ascii/baseline/screen:1')
  Text.redraw_all(Editor_state)
  App.screen.init{width=75, height=80}
  Editor_state = edit.initialize_test_state()
                               --  12345678901234
function test_click_past_end_of_wrapping_line_containing_non_ascii()
  io.write('\ntest_click_past_end_of_wrapping_line_containing_non_ascii')
  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
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  App.screen.check(y, 'am', 'F - test_click_past_end_of_wrapping_line/baseline/screen:3')
  y = y + Editor_state.line_height
  App.screen.check(y, "I'm ad", 'F - test_click_past_end_of_wrapping_line/baseline/screen:2')
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.init{width=75, height=80}
  Editor_state = edit.initialize_test_state()
                               --  12345678901234
function test_click_on_wrapping_line_rendered_from_partway_at_top_of_screen()
  io.write('\ntest_click_on_wrapping_line_rendered_from_partway_at_top_of_screen')
  -- display a wrapping line from its second screen line
  Editor_state.lines = load_array{"madam I'm adam"}
  Editor_state.cursor1 = {line=1, pos=8}
  Editor_state.screen_top1 = {line=1, pos=7}
  Editor_state.screen_bottom1 = {}
  y = y + Editor_state.line_height
  -- click past end of second screen line
  -- cursor moves to end of screen line
end
  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')
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, "I'm ad", 'F - test_click_on_wrapping_line_rendered_from_partway_at_top_of_screen/baseline/screen:2')
  Text.redraw_all(Editor_state)
  App.screen.init{width=75, height=80}
  Editor_state = edit.initialize_test_state()
                               --  12345678901234
  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')
  edit.run_after_mouse_click(Editor_state, App.screen.width-2,y-2, 1)
  y = y + Editor_state.line_height
  App.screen.check(y, "I'm ad", 'F - test_click_on_wrapping_line/baseline/screen:2')
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  App.screen.init{width=75, height=80}
  Editor_state = edit.initialize_test_state()
                               --  12345678901234
  App.screen.check(y, '’m a', 'F - test_draw_wrapping_text_containing_non_ascii/screen:3')
  App.screen.check(y, 'am I', 'F - test_draw_wrapping_text_containing_non_ascii/screen:2')
  Editor_state.lines = load_array{'madam I’m adam', 'xyz'}  -- notice the non-ASCII apostrophe
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'mad', 'F - test_draw_wrapping_text_containing_non_ascii/screen:1')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  App.screen.check(y, 'ijk', 'F - test_draw_text_wrapping_within_word/screen:3')
  y = y + Editor_state.line_height
  App.screen.check(y, 'e fgh', 'F - test_draw_text_wrapping_within_word/screen:2')
  Editor_state.lines = load_array{'abcd e fghijk', 'xyz'}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
end
function test_click_with_mouse_on_wrapping_line()
  io.write('\ntest_click_with_mouse_on_wrapping_line')
  -- display two lines with cursor on one of them
  App.screen.init{width=50, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def ghi jkl mno pqr stu'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=20}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- click on the other line
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  -- cursor moves
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse_on_wrapping_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_click_with_mouse_on_wrapping_line/cursor:pos')
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  Editor_state.lines = load_array{'abc def ghi', 'jkl'}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  App.screen.check(y, 'fgh', 'F - test_draw_wrapping_text/screen:3')
  y = y + Editor_state.line_height
  App.screen.check(y, 'de', 'F - test_draw_wrapping_text/screen:2')
  Editor_state.lines = load_array{'abc', 'defgh', 'xyz'}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  y = y + Editor_state.line_height
  y = y + Editor_state.line_height
  Editor_state.lines = load_array{'abc', 'def', 'ghi'}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
function test_click_with_mouse()
  -- display two lines with cursor on one of them
  App.screen.init{width=50, height=80}
  -- click on the other line
  -- cursor moves
end
end
function test_click_with_mouse_takes_margins_into_account()
  io.write('\ntest_click_with_mouse_takes_margins_into_account')
  -- display two lines with cursor on one of them
  App.screen.init{width=100, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.left = 50  -- occupy only right side of screen
  Editor_state.lines = load_array{'abc', 'def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- click on the other line
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  -- cursor moves
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse_takes_margins_into_account/cursor:line')
end
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_click_with_mouse_takes_margins_into_account/cursor:pos')
function test_click_with_mouse_on_empty_line()
  io.write('\ntest_click_with_mouse_on_empty_line')
  -- display two lines with the first one empty
  App.screen.init{width=50, height=80}
  -- click on the empty line
  -- cursor moves
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse_on_empty_line/cursor')
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  Editor_state.lines = load_array{'', 'def'}
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
function test_click_with_mouse_to_left_of_line()
  io.write('\ntest_click_with_mouse_to_left_of_line')
  -- display a line with the cursor in the middle
  App.screen.init{width=50, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=3}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  -- click to the left of the line
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left-4,Editor_state.top+5, 1)
  -- cursor moves to start of line
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse_to_left_of_line/cursor:line')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_click_with_mouse_to_left_of_line/cursor:pos')
end
  check_eq(Editor_state.cursor1.line, 1, 'F - test_click_with_mouse/cursor:line')
  edit.draw(Editor_state)
  edit.run_after_mouse_click(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  Editor_state.lines = load_array{'abc', 'def'}
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  io.write('\ntest_click_with_mouse')
end
function test_press_ctrl()
  io.write('\ntest_press_ctrl')
  -- press ctrl while the cursor is on text
  App.screen.init{width=50, height=80}
end
function test_move_left()
  io.write('\ntest_move_left')
  check_eq(Editor_state.cursor1.pos, 1, 'F - test_move_left')
end
function test_move_right()
  io.write('\ntest_move_right')
  App.screen.init{width=120, height=60}
  check_eq(Editor_state.cursor1.pos, 2, 'F - test_move_right')
  Editor_state.lines = load_array{'a'}
  Editor_state.cursor1 = {line=1, pos=1}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'right')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'a'}
  Editor_state.cursor1 = {line=1, pos=2}
  edit.draw(Editor_state)
  edit.run_after_keychord(Editor_state, 'left')
  Text.redraw_all(Editor_state)
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{''}
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.run_after_keychord(Editor_state, 'C-m')
  Text.redraw_all(Editor_state)
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{}
  Text.redraw_all(Editor_state)
  edit.draw(Editor_state)
  edit.run_after_textinput(Editor_state, 'a')
  local y = Editor_state.top
  Editor_state = edit.initialize_test_state()
function test_initial_state()
  io.write('\ntest_initial_state')
  App.screen.init{width=120, height=60}
  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')
end
end
function test_backspace_from_start_of_final_line()
  io.write('\ntest_backspace_from_start_of_final_line')
  -- display final line of text with cursor at start of it
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def'}
  Editor_state.screen_top1 = {line=2, pos=1}
  Editor_state.cursor1 = {line=2, pos=1}
  Text.redraw_all(Editor_state)
  -- backspace scrolls up
  edit.run_after_keychord(Editor_state, 'backspace')
  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')
  Editor_state.lines = load_array{}
  Text.redraw_all(Editor_state)
  edit.draw(Editor_state)
  Editor_state = edit.initialize_test_state()