@Test
public void testToKey() {

  Assert.assertNull(SpanUtil.toKey(null));
  Assert.assertEquals(new Key("row"), SpanUtil.toKey(new RowColumn("row")));
  Assert.assertEquals(new Key("row", "cf"),
      SpanUtil.toKey(new RowColumn("row", new Column("cf"))));
  Assert.assertEquals(new Key("row", "cf", "cq"),
      SpanUtil.toKey(new RowColumn("row", new Column("cf", "cq"))));
  Assert.assertEquals(new Key("row", "cf", "cq", "cv"),
      SpanUtil.toKey(new RowColumn("row", new Column("cf", "cq", "cv"))));
}