EmptyClass extends MessageClass<Empty> { public static EmptyClass instance() { return INSTANCE; } private  EmptyClass(); static EmptyClass instance(); @Override String toString();  }
@Test @DisplayName("be serializable") void serialize() { SerializableTester.reserializeAndAssert(EmptyClass.instance()); }
@Test @DisplayName("return the same instance") void sameInstance() { assertSame(EmptyClass.instance(), EmptyClass.instance()); }