.addEqualityGroup(Equivalence.equals().onResultOf(Functions.toStringFunction()))
        .addEqualityGroup(Equivalence.identity().onResultOf(Functions.identity()))
        .testEquals();
  }

  public void testEquivalentTo() {
    Predicate<@Nullable Object> equalTo1 = Equivalence.equals().equivalentTo("1");
    assertTrue(equalTo1.apply("1"));
    assertFalse(equalTo1.apply("2"));
    assertFalse(equalTo1.apply(null));