public void RegisterFactory_WithSingleton_Should_Return_OneInstance()
        {
            var resolver = new SimpleInjectorDependencyResolver();

            resolver.RegisterFactory(typeof(Class6), () => new Class6(), LifetimeScope.Singleton);

            var result        = resolver.Resolve <Class6>();
            var anotherResult = resolver.Resolve <Class6>();

            Assert.IsNotNull(result);
            Assert.AreEqual(result, anotherResult);
            Assert.AreEqual(1, Class6.Instances);
        }