Predicate<String> post = SerializableTester.reserializeAndAssert(pre);
    assertEquals(pre.apply("foo"), post.apply("foo"));
    assertEquals(pre.apply(null), post.apply(null));
  }

  public void testNotNull_apply() {
    Predicate<@Nullable Integer> notNull = Predicates.notNull();
    assertFalse(notNull.apply(null));
    assertTrue(notNull.apply(1));
  }

  public void testNotNull_equality() {