[Subject(typeof(MembershipService), "Registering a user")]
    public class when_member_data_is_totally_correct : Membership_service_subscription_context
    {
        Because of = () =>
            suo.Register(signup);

        It should_save_member_to_repository = () =>
            memberRepository.Verify(r => r.Add(Moq.It.Is<Member>(m => m.Username == "non.exists")));
    }

    [Subject(typeof(MembershipService), "Registering a user")]
    public class when_member_data_is_submited : Membership_service_subscription_context
    {
        Because of = () =>
            suo.Register(signup);

        It should_check_with_repository_if_user_already_exists = () =>
            memberRepository.Verify(r => r.GetByUsername(Moq.It.IsAny<string>()));
    }

    [Subject(typeof(MembershipService), "Registering a user")]
    public class when_username_is_already_taken : Membership_service_subscription_context
    {
        static Exception exception;

        Because of = () => {
            signup.Username = "username";
            exception = Catch.Exception(() => suo.Register(signup));
        };

        It should_throw_a_validation_exception = () =>
            exception.ShouldBeOfType<ValidationException>();
    }

    public class Membership_service_subscription_context
    {
        protected static Mock<IMemberRepository> memberRepository = new Mock<IMemberRepository>();
        protected static IMembershipService suo;
        protected static SignUpForm signup;

        protected static Member member;

        Establish context = () =>
        {
            member = new Member("username", "first name", "last name", string.Empty, DateTime.Now, Gender.Male, MemberType.Student);
            signup = new SignUpForm
                {
                    Username = "non.exists",
                    FirstName = "first name",
                    LastName = "last name",
                    Email = "email@mail.com",
                    Password = "password",
                    RepeatPassword = "password",
                    BirthDate = DateTime.Now,
                    SchoolId = 1
                };

            memberRepository.Setup(r => r.GetByUsername(member.Username)).Returns(member);
            memberRepository.Setup(r => r.GetByUsername("non.exist")).Returns(() => null);

            suo = new MembershipService(memberRepository.Object);
        };
    }