@Test
public void testCompare() {

  Column c1 = new Column("a", "b");
  Column c2 = new Column("a", "c");
  Column c3 = new Column("a", "b", "d");
  Column c4 = new Column("a");
  Column c5 = Column.EMPTY;
  Column c6 = new Column("a", "b");
  Assert.assertEquals(-1, c1.compareTo(c2));
  Assert.assertEquals(1, c2.compareTo(c1));
  Assert.assertEquals(0, c1.compareTo(c6));
  Assert.assertEquals(1, c1.compareTo(c5));
  Assert.assertEquals(-1, c4.compareTo(c1));
  Assert.assertEquals(-1, c1.compareTo(c3));
  Assert.assertEquals(1, c4.compareTo(c5));
  Assert.assertEquals(-1, c3.compareTo(c2));
}