public void FactoryShouldShouldReturnExistinInstanceHavingUsedState()
        {
            List <Flyweight> list = new List <Flyweight>()
            {
                new Flyweight("F1"),
                new Flyweight("F2")
            };

            FlyweightFactory factory = new FlyweightFactory(list);

            Flyweight instance = factory.GetFlyweight();

            instance.Should().NotBeNull();
            instance.State.Should().BeEquivalentTo("used");
        }