@Test
public void testAddAndRemoveScalarColumns() {

  String removedKey = "removedKey";
  String addedKey = "addedKey";
  Map<String, String> previousColumns =
      ImmutableMap.of(
          removedKey, "removedValue",
          SHARED_KEY, "sharedValue");
  Map<String, String> currentColumns =
      ImmutableMap.of(
          SHARED_KEY, "sharedValue",
          addedKey, "addedValue");
  assertEquals(
      ImmutableSet.of(removedKey, addedKey),
      Mutation.getUpdatedColumns(previousColumns, currentColumns));
}