@Test
public void testAppendCell() {

  column1.appendCell("1923-10-20T10:15:30");
  column1.appendCell("1924-12-10T10:15:30");
  column1.appendCell("2015-12-05T10:15:30");
  column1.appendCell("2015-12-20T10:15:30");
  assertEquals(4, column1.size());
  LocalDateTime date = LocalDateTime.now();
  column1.append(date);
  assertEquals(5, column1.size());
}