@Test
public void testUpdateScalarColumnValues() {

  String updatedKey = "updatedKey";
  Map<String, String> previousColumns =
      ImmutableMap.of(
          SHARED_KEY, "sharedValue",
          updatedKey, "previousValue");
  Map<String, String> currentColumns =
      ImmutableMap.of(
          SHARED_KEY, "sharedValue",
          updatedKey, "currentValue");
  assertEquals(
      ImmutableSet.of(updatedKey), Mutation.getUpdatedColumns(previousColumns, currentColumns));
}