equivalenceMock.expectHash(group2Item1, 2);
    equivalenceMock.expectHash(group2Item2, 2);

    equivalenceMock.replay();

    tester
        .addEquivalenceGroup(group1Item1, group1Item2)
        .addEquivalenceGroup(group2Item1, group2Item2)
        .test();
  }

  public void testTest_symmetric() {
    Object group1Item1 = new TestObject(1, 1);
    Object group1Item2 = new TestObject(1, 2);

    equivalenceMock.expectHash(group2Item1, 2);
    equivalenceMock.expectHash(group2Item2, 2);

    equivalenceMock.replay();

    tester
        .addEquivalenceGroup(group1Item1, group1Item2)
        .addEquivalenceGroup(group2Item1, group2Item2)
        .test();
  }

  public void testTest_symmetric() {
    Object group1Item1 = new TestObject(1, 1);
    Object group1Item2 = new TestObject(1, 2);

        .addEquivalenceGroup(new Integer(42_000_000), 42_000_000)
        .addEquivalenceGroup("a")
        .test();
  }

  public void testIdentityEquivalent() {
    EquivalenceTester.of(Equivalence.identity())
        .addEquivalenceGroup(new Integer(42_000_000))
        .addEquivalenceGroup(new Integer(42_000_000))
        .addEquivalenceGroup("a")
        .test();
  }

   * objects in any other equivalence group added to this tester.
   */
  @CanIgnoreReturnValue
  public EquivalenceTester<T> addEquivalenceGroup(T first, T... rest) {
    addEquivalenceGroup(Lists.asList(first, rest));
    return this;
  }

  @CanIgnoreReturnValue
  public EquivalenceTester<T> addEquivalenceGroup(Iterable<T> group) {
    delegate.addRelatedGroup(group);
    items.addAll(ImmutableList.copyOf(group));
    return this;
  }

   * objects in any other equivalence group added to this tester.
   */
  @CanIgnoreReturnValue
  public EquivalenceTester<T> addEquivalenceGroup(T first, T... rest) {
    addEquivalenceGroup(Lists.asList(first, rest));
    return this;
  }

  @CanIgnoreReturnValue
  public EquivalenceTester<T> addEquivalenceGroup(Iterable<T> group) {
    delegate.addRelatedGroup(group);
    items.addAll(ImmutableList.copyOf(group));
    return this;
  }