new TestDatum("A", 2),
            new TestDatum("B", 1),
            new TestDatum("C", 1),
            new TestDatum("C", 2))
        .inOrder();
  }

  public void testMergeSorted_stable_allEqual() {
    ImmutableList<TestDatum> first = ImmutableList.of(new TestDatum("A", 1), new TestDatum("A", 2));
    ImmutableList<TestDatum> second =
        ImmutableList.of(new TestDatum("A", 3), new TestDatum("A", 4));