new ClassSanityTester()
        .setDefault(Duration.class, Duration.ofSeconds(1))
        .forAllPublicStaticMethods(Suppliers.class)
        .testSerializable();
  }

  public void testOfInstance_equals() {
    new EqualsTester()
        .addEqualityGroup(Suppliers.ofInstance("foo"), Suppliers.ofInstance("foo"))
        .addEqualityGroup(Suppliers.ofInstance("bar"))
        .testEquals();
  }