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}
  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, 'def', 'F - test_backspace_can_scroll_up/baseline/screen:1')
  y = y + line_height
  App.screen.check(y, 'ghi', 'F - test_backspace_can_scroll_up/baseline/screen:2')
  y = y + line_height
  App.screen.check(y, 'jkl', 'F - test_backspace_can_scroll_up/baseline/screen:3')
  -- after hitting backspace the screen scrolls up by one line
  App.run_after_keychord('backspace')
  check_eq(Screen_top1.line, 1, 'F - test_backspace_can_scroll_up/screen_top')
  check_eq(Cursor1.line, 1, 'F - test_backspace_can_scroll_up/cursor')
  y = screen_top_margin
  App.screen.check(y, 'abcdef', 'F - test_backspace_can_scroll_up/screen:1')
  y = y + line_height
  App.screen.check(y, 'ghi', 'F - test_backspace_can_scroll_up/screen:2')
  y = y + line_height
  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
  App.screen.init{width=25+30, height=60}
  Lines = load_array{'abc', 'def', 'ghi jkl', 'mno'}
  Line_width = App.screen.width
  Cursor1 = {line=3, pos=5}
  Screen_top1 = {line=3, pos=5}
  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, 'jkl', 'F - test_backspace_can_scroll_up_screen_line/baseline/screen:1')
  y = y + line_height
  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
  App.run_after_keychord('backspace')
  y = screen_top_margin
  App.screen.check(y, 'ghijk', 'F - test_backspace_can_scroll_up_screen_line/screen:1')
  y = y + line_height
  App.screen.check(y, 'l', 'F - test_backspace_can_scroll_up_screen_line/screen:2')
  y = y + line_height
  App.screen.check(y, 'mno', 'F - test_backspace_can_scroll_up_screen_line/screen:3')
  check_eq(Screen_top1.line, 3, 'F - test_backspace_can_scroll_up_screen_line/screen_top')
  check_eq(Screen_top1.pos, 1, 'F - test_backspace_can_scroll_up_screen_line/screen_top')
  check_eq(Cursor1.line, 3, 'F - test_backspace_can_scroll_up_screen_line/cursor:line')
  check_eq(Cursor1.pos, 4, 'F - test_backspace_can_scroll_up_screen_line/cursor:pos')

    end
    if Cursor1.line < Screen_top1.line or (Cursor1.line == Screen_top1.line and Cursor1.pos < Screen_top1.pos) then
      local top2 = Text.to2(Screen_top1)
      top2 = Text.previous_screen_line(top2)
      Screen_top1 = Text.to1(top2)

    assert(Cursor1.line > Screen_top1.line or (Cursor1.line == Screen_top1.line and Cursor1.pos >= Screen_top1.pos))