edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)  -- populate line_cache.startpos for each line
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)  -- populate line_cache.startpos for each line
  edit.draw(Editor_state, Text_color)  -- populate line_cache.startpos for each line
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)  -- populate line_cache.startpos for each line
  edit.draw(Editor_state, Text_color)  -- populate line_cache.startpos for each line
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  Editor_state.lines = load_array{'abc', 'def', 'ghi', '’deg'}  -- contains unicode quote in final line
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  edit.draw(Editor_state, Text_color)
  -- search for empty string
  edit.run_after_keychord(Editor_state, 'C-f', 'f')
  edit.run_after_keychord(Editor_state, 'down', 'down')
  -- no crash
end
  -- search for empty string
  edit.run_after_keychord(Editor_state, 'C-f', 'f')
  edit.run_after_keychord(Editor_state, 'down', 'down')
  -- no crash
end
function test_search_downwards_from_final_pos_of_line()
  App.screen.init{width=120, 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=3}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- search upwards for a string
  edit.run_after_keychord(Editor_state, 'C-f', 'f')
  edit.run_after_text_input(Editor_state, 'a')
  edit.run_after_keychord(Editor_state, 'up', 'up')
  -- cursor wraps
  check_eq(Editor_state.cursor1.line, 1, '1/cursor:line')
  check_eq(Editor_state.cursor1.pos, 6, '1/cursor:pos')
end
function test_search_downwards_from_end_of_line()
  App.screen.init{width=120, 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=4}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- search for a string
  edit.run_after_keychord(Editor_state, 'C-f', 'f')
  edit.run_after_text_input(Editor_state, 'a')
  edit.run_after_keychord(Editor_state, 'return', 'return')
  -- cursor wraps
  check_eq(Editor_state.cursor1.line, 1, '1/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, '1/cursor:pos')
end
function test_search_wrap_upwards()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc ’abd'}  -- contains unicode quote
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- search for a string
  edit.run_after_keychord(Editor_state, 'C-f', 'f')
  edit.run_after_text_input(Editor_state, 'a')
  -- search for previous occurrence
  edit.run_after_keychord(Editor_state, 'up', 'up')
  check_eq(Editor_state.cursor1.line, 1, '2/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, '2/cursor:pos')
end
function test_search_wrap()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'’abc', 'def'}  -- contains unicode quote in first line
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- search for a string
  edit.run_after_keychord(Editor_state, 'C-f', 'f')
  edit.run_after_text_input(Editor_state, 'd')
  edit.run_after_keychord(Editor_state, 'return', 'return')
  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', 'f')
  edit.run_after_text_input(Editor_state, 'de')
  edit.run_after_keychord(Editor_state, 'down', 'down')
  edit.run_after_keychord(Editor_state, 'return', 'return')
  check_eq(Editor_state.cursor1.line, 4, '2/cursor:line')
  check_eq(Editor_state.cursor1.pos, 2, '2/cursor:pos')
end
function test_search_upwards()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'’abc', 'abd'}  -- contains unicode quote
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- delete selected text
  edit.run_after_text_input(Editor_state, 'x')
  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', 'z')
  edit.run_after_keychord(Editor_state, 'C-z', 'z')
  -- selection is restored
  check_eq(Editor_state.selection1.line, 1, 'line')
  check_eq(Editor_state.selection1.pos, 2, 'pos')
end
function test_search()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  edit.run_after_text_input(Editor_state, 'g')
  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
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'defg', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'xyz', 'baseline/screen:3')
  -- undo
  edit.run_after_keychord(Editor_state, 'C-z', 'z')
  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, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'xyz', 'screen:3')
end
function test_undo_delete_text()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'defg', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=5}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- delete a character
  edit.run_after_keychord(Editor_state, 'backspace', 'backspace')
  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, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'xyz', 'baseline/screen:3')
  -- undo
--?   -- after undo, the backspaced key is selected
  edit.run_after_keychord(Editor_state, 'C-z', 'z')
  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, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'defg', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'xyz', 'screen:3')
end
function test_undo_restores_selection()
  -- display a line of text with some part selected
  App.screen.init{width=75, 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=1}
  Editor_state.selection1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  local y = Editor_state.top
  local y = Editor_state.top
  App.screen.check(y, 'def', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:2')
  y = y + Editor_state.line_height
  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', 'backspace')
  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, 'abcdef', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'screen:3')
end
function test_backspace_can_scroll_up_screen_line()
  -- display lines starting from second screen line of a 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 jkl', 'mno'}
  Text.redraw_all(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'abc def ghi ', 'baseline1/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl mno pqr ', 'baseline1/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'xyz', 'baseline1/screen:3')
  -- add to the line until it's wrapping over 3 screen lines
  edit.run_after_text_input(Editor_state, 's')
  edit.run_after_text_input(Editor_state, 't')
  edit.run_after_text_input(Editor_state, 'u')
  check_eq(Editor_state.cursor1.pos, 28, 'cursor:pos')
  y = Editor_state.top
  App.screen.check(y, 'abc def ghi ', 'baseline2/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl mno pqr ', 'baseline2/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'stu', 'baseline2/screen:3')
  -- try to move the cursor earlier in the third screen line by clicking the mouse
  edit.run_after_mouse_release(Editor_state, Editor_state.left+2,Editor_state.top+Editor_state.line_height*2+5, 1)
  -- cursor should move
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 25, 'cursor:pos')
end
function test_backspace_can_scroll_up()
  -- display the lines 2/3/4 with the cursor on line 2
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  local y = Editor_state.top
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  local y = Editor_state.top
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:3')
  -- after typing something the line wraps and the screen scrolls down
  edit.run_after_text_input(Editor_state, 'j')
  edit.run_after_text_input(Editor_state, 'k')
  edit.run_after_text_input(Editor_state, 'l')
  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, 'def', 'screen:1')
  y = y + Editor_state.line_height
  -- after hitting the inserting_text key the screen does not scroll down
  edit.run_after_text_input(Editor_state, 'a')
  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, 'a', 'screen:1')
end
function test_typing_on_bottom_line_scrolls_down()
  -- display a few lines with cursor on bottom line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  local 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', 'return')
  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, 'j', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'kl', 'screen:2')
end
function test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom()
  -- display just an empty bottom line on screen
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', ''}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:3')
  -- after hitting the enter key the screen scrolls down
  edit.run_after_keychord(Editor_state, 'return', 'return')
  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, 'def', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'g', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'hi', 'screen:3')
end
function test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom()
  -- display just the bottom line on screen
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=4, pos=2}
  Editor_state.screen_top1 = {line=4, pos=1}
  local y = Editor_state.top
  local y = Editor_state.top
  App.screen.check(y, 'ghi', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'baseline/screen:2')
  y = y + Editor_state.line_height
  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', 'pageup')
  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, 'abc ', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', '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()
  -- display a few lines starting from the middle of a line (Editor_state.cursor1.pos > 1)
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def', 'ghi jkl', 'mno'}
  Text.redraw_all(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'def', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:2')
  -- after pageup the cursor goes to first line
  edit.run_after_keychord(Editor_state, 'pageup', 'pageup')
  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, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:2')
end
function test_pageup_scrolls_up_by_screen_line()
  -- display the first three lines with the cursor on the bottom 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', 'jkl', 'mno'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  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', 'up')
  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, 'abc', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:3')
end
function test_pageup()
  App.screen.init{width=120, height=45}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  -- initially the last two lines are displayed
  local y = Editor_state.top
  App.screen.check(y, 'ghi', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'baseline/screen:2')
  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', 'up')
  y = Editor_state.top
  App.screen.check(y, 'def', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:2')
  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()
  -- display a screenful of text with an empty line just above it outside the screen
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'', 'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=2, pos=1}
  local y = Editor_state.top
  local y = Editor_state.top
  App.screen.check(y, 'def', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:2')
  y = y + Editor_state.line_height
  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', 'up')
  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, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:3')
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  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', 'up')
  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, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:3')
end
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  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', 'down')
  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, 'def', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'screen:3')
end
function test_down_arrow_scrolls_down_by_one_screen_line()
  -- display the first three lines with the cursor on the bottom line
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  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', 'down')
  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, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:3')
end
  -- pagedown makes no change
  edit.run_after_keychord(Editor_state, 'pagedown', 'pagedown')
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top:line')
  local y = Editor_state.top
  App.screen.check(y, 'abc ', 'baseline/screen:1')
  y = y + Editor_state.line_height
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  -- after pagedown the bottom line becomes the top
  edit.run_after_keychord(Editor_state, 'pagedown', 'pagedown')
  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', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:2')
  -- try to cut without selecting text
  edit.run_after_keychord(Editor_state, 'C-x', 'x')
  -- no crash
  check_nil(Editor_state.selection1.line, 'check')
end
function test_pagedown()
  App.screen.init{width=120, height=45}
  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=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- initially the first two lines are displayed
  -- select all
  App.fake_key_press('lctrl')
  edit.run_after_keychord(Editor_state, 'C-a', 'a')
  App.fake_key_release('lctrl')
  edit.key_release(Editor_state, 'lctrl')
  -- selection
  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, 8, 'cursor:pos')
end
function test_cut_without_selection()
  -- display a few lines
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.selection1 = {}
  -- click on first location
  edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  edit.run_after_mouse_release(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  -- hold down shift and click on a second location
  App.fake_key_press('lshift')
  edit.run_after_mouse_press(Editor_state, Editor_state.left+20,Editor_state.top+5, 1)
  edit.run_after_mouse_release(Editor_state, Editor_state.left+20,Editor_state.top+Editor_state.line_height+5, 1)
  -- hold down shift and click at a third location
  App.fake_key_press('lshift')
  edit.run_after_mouse_press(Editor_state, Editor_state.left+20,Editor_state.top+5, 1)
  edit.run_after_mouse_release(Editor_state, Editor_state.left+8,Editor_state.top+Editor_state.line_height+5, 1)
  App.fake_key_release('lshift')
  -- selection is between first and third location. forget the second location, not the first.
  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
function test_select_all_text()
  -- display a single line of text
  App.screen.init{width=75, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- click on first location
  edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  edit.run_after_mouse_release(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  -- hold down shift and click somewhere else
  App.fake_key_press('lshift')
  edit.run_after_mouse_press(Editor_state, Editor_state.left+20,Editor_state.top+5, 1)
  edit.run_after_mouse_release(Editor_state, Editor_state.left+20,Editor_state.top+Editor_state.line_height+5, 1)
  App.fake_key_release('lshift')
  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()
  App.screen.init{width=50, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'xyz'}
  Text.redraw_all(Editor_state)
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.selection1 = {}
  local y = Editor_state.top
  edit.run_after_mouse_press(Editor_state, Editor_state.left+8,5, 1)
  -- selection is at screen top
  check(Editor_state.selection1.line ~= nil, 'selection:line-not-nil')
  check_eq(Editor_state.selection1.line, 2, 'selection:line')
  check_eq(Editor_state.selection1.pos, 3, 'selection:pos')
end
function test_select_text_using_mouse_starting_below_text()
  -- I'd like to test what happens when a mouse click is below some page of
  -- text, potentially even in the middle of a line.
  -- However, it's brittle to set up a text line boundary just right.
  -- So I'm going to just check things below the bottom of the final line of
  -- text when it's in the middle of the screen.
  -- final screen line ends in the middle of screen
  App.screen.init{width=50, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abcde'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- press mouse above first line of text
  edit.run_after_mouse_press(Editor_state, Editor_state.left+8,5, 1)
  check(Editor_state.selection1.line ~= nil, 'selection:line-not-nil')
  check_eq(Editor_state.selection1.line, 1, 'selection:line')
  check_eq(Editor_state.selection1.pos, 1, 'selection:pos')
end
function test_select_text_using_mouse_starting_above_text_wrapping_line()
  -- first screen line starts in the middle of a line
  App.screen.init{width=50, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'defgh', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=5}
  Editor_state.screen_top1 = {line=2, pos=3}
  -- press mouse above first line of text
  -- press and hold on first location
  edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  -- drag and release somewhere else
  edit.run_after_mouse_release(Editor_state, Editor_state.left+20,Editor_state.top+Editor_state.line_height+5, 1)
  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_starting_above_text()
  App.screen.init{width=50, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.selection1 = {}
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  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', 'v')
  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, 'axy', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'zbc', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:3')
end
function test_select_text_using_mouse()
  App.screen.init{width=50, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.selection1 = {}
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:3')
  -- hitting the enter key splits the line
  edit.run_after_keychord(Editor_state, 'return', 'return')
  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, 'a', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'bc', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:3')
end
function test_insert_newline_at_start_of_line()
  -- display a line
  App.screen.init{width=Editor_state.left+30, 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=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- hitting the enter key splits the line
  edit.run_after_keychord(Editor_state, 'return', 'return')
  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()
  -- display a few lines
  App.screen.init{width=Editor_state.left+30, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  edit.run_after_text_input(Editor_state, 'g')
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  local y = Editor_state.top
  App.screen.check(y, 'def', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:2')
  y = y + Editor_state.line_height
  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', 'backspace')
  -- page scrolls up
  check_eq(Editor_state.screen_top1.line, 1, 'check')
  check_eq(Editor_state.lines[1].data, 'ahi', 'data')
end
function test_edit_wrapping_text()
  App.screen.init{width=50, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=4}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- set clipboard
  App.clipboard = 'xyz'
  -- paste selection
  edit.run_after_keychord(Editor_state, 'C-v', 'v')
  -- selection is reset since shift key is not pressed
  -- selection includes the newline, so it's also deleted
  check_eq(Editor_state.lines[1].data, 'xyzdef', 'check')
end
function test_deleting_selection_may_scroll()
  -- display lines 2/3/4
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=2}
  Editor_state.screen_top1 = {line=2, pos=1}
  -- press a key
  edit.run_after_keychord(Editor_state, 'C-x', 'x')
  check_eq(App.clipboard, 'a', 'clipboard')
  -- selected text is deleted
  check_eq(Editor_state.lines[1].data, 'bc', 'data')
end
function test_paste_replaces_selection()
  -- display a line of text with a selection
  App.screen.init{width=75, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.selection1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- copy selection
  edit.run_after_keychord(Editor_state, 'C-c', 'c')
  check_eq(App.clipboard, 'a', 'clipboard')
  -- selection is reset since shift key is not pressed
  check(Editor_state.selection1.line, 'check')
end
function test_cut()
  -- display a line of text with some part selected
  App.screen.init{width=75, 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=1}
  Editor_state.selection1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- mimic precise keypresses for a capital letter
  App.fake_key_press('lshift')
  edit.keychord_press(Editor_state, 'd', 'd')
  edit.text_input(Editor_state, 'D')
  edit.key_release(Editor_state, 'd')
  App.fake_key_release('lshift')
  -- selected text is deleted and replaced with the key
  check_nil(Editor_state.selection1.line, 'check')
  check_eq(Editor_state.lines[1].data, 'Dbc', 'data')
end
function test_copy_does_not_reset_selection()
  -- display a line of text with a selection
  App.screen.init{width=75, 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=1}
  Editor_state.selection1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- press a key
  edit.run_after_text_input(Editor_state, 'x')
  -- selected text is deleted and replaced with the key
  check_eq(Editor_state.lines[1].data, 'xbc', 'check')
end
function test_edit_with_shift_key_deletes_selection()
  -- display a line of text with some part selected
  App.screen.init{width=75, 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=1}
  Editor_state.selection1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- press an arrow key without shift
  edit.run_after_keychord(Editor_state, 'right', 'right')
  -- no change to data, selection is reset
  check_nil(Editor_state.selection1.line, 'check')
  check_eq(Editor_state.lines[1].data, 'abc', 'data')
end
function test_edit_deletes_selection()
  -- display a line of text with some part selected
  App.screen.init{width=75, 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=1}
  Editor_state.selection1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  -- select a letter
  App.fake_key_press('lshift')
  edit.run_after_keychord(Editor_state, 'S-right', 'right')
  App.fake_key_release('lshift')
  edit.key_release(Editor_state, 'lshift')
  -- selection persists even after shift is released
  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()
  -- display a line of text with some part selected
  App.screen.init{width=75, 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=1}
  Editor_state.selection1 = {line=1, pos=2}
  Editor_state.screen_top1 = {line=1, pos=1}
  local y = Editor_state.top
  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 (one more than final character shown)
  check_eq(Editor_state.cursor1.pos, 21, 'cursor')
end
function test_select_text()
  -- display a line of text
  App.screen.init{width=75, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  local y = Editor_state.top
  App.screen.check(y, 'madam ', 'baseline/screen:1')
  y = y + Editor_state.line_height
  local y = Editor_state.top
  App.screen.check(y, 'madam ', 'baseline/screen:1')
  y = y + Editor_state.line_height
  local y = Editor_state.top
  local y = Editor_state.top
  App.screen.check(y, 'madam ', 'baseline/screen:1')
  y = y + Editor_state.line_height
  local y = Editor_state.top
  local y = Editor_state.top
  App.screen.check(y, 'abcd ', 'screen:1')
  y = y + Editor_state.line_height
  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, '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
  App.screen.init{width=60, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abcd e fghijk', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  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, '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_click_on_wrapping_line_takes_margins_into_account()
  -- display two screen 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}
  -- click on the other line
  local y = Editor_state.top
  App.screen.check(y, 'abc ', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def ', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:3')
end
function test_click_on_wrapping_line()
  -- display two screen 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}
  -- click on the other line
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  local y = Editor_state.top
  App.screen.check(y, 'abc', 'screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'def', 'screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'screen:3')
end
function test_draw_wrapping_text()
  App.screen.init{width=50, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'defgh', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  edit.run_after_mouse_click(Editor_state, Editor_state.left+8,Editor_state.top+50, 1)
  -- cursor goes to bottom
  check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
  check_eq(Editor_state.cursor1.pos, 4, 'cursor:pos')
  -- selection remains empty
  check_nil(Editor_state.selection1.line, 'selection is empty to avoid perturbing future edits')
end
function test_draw_text()
  App.screen.init{width=120, 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=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  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, 'cursor')
  -- selection remains empty
  check_nil(Editor_state.selection1.line, 'selection is empty to avoid perturbing future edits')
end
function test_click_below_final_line_of_file()
  -- display one line
  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=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.selection1 = {}
  -- click below first line
  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, '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_click_on_empty_line()
  -- display two lines with the first one empty
  App.screen.init{width=50, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'', 'def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.selection1 = {}
  -- click on the empty line
  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, '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
function test_click_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.selection1 = {}
  -- click on the other line
  edit.run_after_mouse_release(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
  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_nil(Editor_state.selection1.line, 'selection:line')
  check_nil(Editor_state.selection1.pos, 'selection:pos')
end
function test_click_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.selection1 = {}
  -- click to the left of the line
  edit.run_after_keychord(Editor_state, 'M-right', 'right')
  check_eq(Editor_state.cursor1.line, 2, 'line')
  check_eq(Editor_state.cursor1.pos, 4, 'pos')
end
function test_click_moves_cursor()
  App.screen.init{width=50, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def', 'xyz'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  Editor_state.selection1 = {}
  edit.run_after_keychord(Editor_state, 'M-right', 'right')
  check_eq(Editor_state.cursor1.pos, 9, 'check')
end
function test_move_past_end_of_word_on_next_line()
  App.screen.init{width=120, 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=8}
  edit.run_after_keychord(Editor_state, 'M-right', 'right')
  check_eq(Editor_state.cursor1.pos, 4, 'check')
end
function test_skip_multiple_spaces_to_next_word()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc  def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=4}  -- at the start of second word
  edit.run_after_keychord(Editor_state, 'M-right', 'right')
  check_eq(Editor_state.cursor1.pos, 8, 'check')
end
function test_skip_past_tab_to_next_word()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc\tdef'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}  -- at the space between words
  edit.run_after_keychord(Editor_state, 'M-right', 'right')
  check_eq(Editor_state.cursor1.pos, 4, 'check')
end
function test_skip_to_next_word()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=4}  -- at the space between words
  edit.run_after_keychord(Editor_state, 'M-left', 'left')
  check_eq(Editor_state.cursor1.line, 1, 'line')
  check_eq(Editor_state.cursor1.pos, 5, 'pos')
end
function test_move_past_end_of_word()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  edit.run_after_keychord(Editor_state, 'M-left', 'left')
  check_eq(Editor_state.cursor1.pos, 1, 'check')
end
function test_move_to_start_of_word_on_previous_line()
  App.screen.init{width=120, 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=2, pos=1}
  edit.run_after_keychord(Editor_state, 'M-left', 'left')
  check_eq(Editor_state.cursor1.pos, 9, 'check')
end
function test_skip_multiple_spaces_to_previous_word()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc  def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=6}  -- at the start of second word
  edit.run_after_keychord(Editor_state, 'M-left', 'left')
  check_eq(Editor_state.cursor1.pos, 1, 'check')
end
function test_skip_past_tab_to_previous_word()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def\tghi'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=10}  -- within third word
  edit.run_after_keychord(Editor_state, 'M-left', 'left')
  check_eq(Editor_state.cursor1.pos, 1, 'check')
end
function test_skip_to_previous_word()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=5}  -- at the start of second word
  edit.run_after_keychord(Editor_state, 'M-left', 'left')
  check_eq(Editor_state.cursor1.pos, 1, 'check')
end
function test_move_to_start_of_previous_word()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=4}  -- at the space between words
  edit.run_after_keychord(Editor_state, 'right', 'right')
  check_eq(Editor_state.cursor1.line, 2, 'line')
  check_eq(Editor_state.cursor1.pos, 1, 'pos')
end
function test_move_to_start_of_word()
  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}
  edit.run_after_keychord(Editor_state, 'left', 'left')
  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()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=4}  -- past end of line
  edit.run_after_keychord(Editor_state, 'right', 'right')
  check_eq(Editor_state.cursor1.pos, 2, 'check')
end
function test_move_left_to_previous_line()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', 'def'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=2, pos=1}
  edit.run_after_keychord(Editor_state, 'left', 'left')
  check_eq(Editor_state.cursor1.pos, 1, 'check')
end
function test_move_right()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'a'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  edit.run_after_text_input(Editor_state, 'a')
  local y = Editor_state.top
  App.screen.check(y, 'a', 'screen:1')
end
function test_press_ctrl()
  -- press ctrl while the cursor is on text
  App.screen.init{width=50, height=80}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{''}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=1}
  Editor_state.screen_top1 = {line=1, pos=1}
  edit.run_after_keychord(Editor_state, 'C-m', 'm')
end
function test_move_left()
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'a'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=1, pos=2}
  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')