check_eq(Screen_top1.line, 1, 'F - test_up_arrow_moves_cursor/screen_top')

  check_eq(Screen_top1.line, 1, 'F - test_down_arrow_moves_cursor/screen_top')

function test_up_arrow_scrolls_up_to_empty_line()
  io.write('\ntest_up_arrow_scrolls_up_from_empty_line')
  -- display a screenful of text with an empty line just above it outside the screen
  App.screen.init{width=120, height=60}
  Lines = load_array{'', 'abc', 'def', 'ghi', 'jkl'}
  Line_width = 120
  Cursor1 = {line=2, pos=1}
  Screen_top1 = {line=2, pos=1}
  Screen_bottom1 = {}
  Zoom = 1
  local screen_top_margin = 15  -- pixels
  local line_height = math.floor(15*Zoom)  -- pixels
  App.draw()
  local y = screen_top_margin
  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_from_empty_line/baseline/screen:1')
  y = y + line_height
  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_from_empty_line/baseline/screen:2')
  y = y + line_height
  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_from_empty_line/baseline/screen:3')
  -- after hitting the up arrow the screen scrolls up by one line
  App.run_after_keychord('up')
  check_eq(Screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_from_empty_line/screen_top')
  check_eq(Cursor1.line, 1, 'F - test_up_arrow_scrolls_up_from_empty_line/cursor')
  y = screen_top_margin
  -- empty first line
  y = y + line_height
  App.screen.check(y, 'abc', 'F - test_up_arrow_scrolls_up_from_empty_line/screen:2')
  y = y + line_height
  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_from_empty_line/screen:3')
end

--?   print('--')

--?   print('-- nearest', x)

--?     print('nearest', x, '^'..line..'$', left, right)
    if left == right then
      return left
    end

--?     print(x, left, right, curr, currxmin, currxmax)

--?     print('nearest', x, left, right, curr, currxmin, currxmax)

  local line_before_cursor = line_data:sub(1, cursor_pos-1)

--?   print(cursor_pos, #line_data, line_data)
  local cursor_offset = utf8.offset(line_data, cursor_pos)
--?   print(cursor_offset)
  assert(cursor_offset)
  local line_before_cursor = line_data:sub(1, cursor_offset-1)

  local s_before_cursor = s:sub(1, cursor_pos-1)

  local cursor_offset = utf8.offset(s, cursor_pos)
  assert(cursor_offset)
  local s_before_cursor = s:sub(1, cursor_offset-1)