@Test
public void testCompare() {

  RowColumn rc1 = new RowColumn("a", new Column("b"));
  RowColumn rc2 = new RowColumn("b");
  RowColumn rc3 = new RowColumn("a", new Column("c"));
  RowColumn rc4 = new RowColumn("a", new Column("c", "d"));
  Assert.assertEquals(-1, rc1.compareTo(rc2));
  Assert.assertEquals(1, rc2.compareTo(rc1));
  Assert.assertEquals(-1, rc1.compareTo(rc3));
  Assert.assertEquals(-1, rc3.compareTo(rc2));
  Assert.assertEquals(0, rc3.compareTo(rc3));
  Assert.assertEquals(1, rc2.compareTo(RowColumn.EMPTY));
  Assert.assertEquals(-1, rc3.compareTo(rc4));
}