check_eq(#Editor_state.lines, 3, '#lines')
  check_eq(Editor_state.lines[1].data, 'abc', 'lines:1')
  check_eq(Editor_state.lines[2].data, 'def', 'lines:2')
  check_eq(Editor_state.lines[3].data, 'ghi', 'lines:3')
  check_eq(App.filesystem['foo'], 'abc\ndef\n', 'check')