public void GetUserByUserName_WhenUserDoesNotExist_ReturnNull()
        {
            var storageMock = new Mock<IEntityStorage<User>>();
            storageMock.SetupGet(x => x.Entities)
                .Returns(new List<User>());

            var dateTimeServiceMock = new Mock<IDateTimeService>();
            var service = new UserService(storageMock.Object, dateTimeServiceMock.Object) as IUserService;

            var user = service.GetUserByUserName("non existing username");

            Assert.IsNull(user);
        }
        public void GetUserByUserName_WhenUserNameIsNullOrWhiteSpace_ThrowArgumentException(string userName)
        {
            var storageMock = new Mock<IEntityStorage<User>>();
            var dateTimeServiceMock = new Mock<IDateTimeService>();
            var service = new UserService(storageMock.Object, dateTimeServiceMock.Object) as IUserService;

            service.GetUserByUserName(userName);
        }