public async Task Should_Cancel_Registration()
        {
            //Arrange
            var currentUserId = AbpSession.GetUserId();

            await UsingDbContext(async context =>
            {
                var testEvent        = GetTestEvent(context);
                var currentUser      = await context.Users.SingleAsync(u => u.Id == currentUserId);
                var testRegistration = await EventRegistration.CreateAsync(
                    testEvent,
                    currentUser,
                    Substitute.For <IEventRegistrationPolicy>()
                    );

                context.EventRegistrations.Add(testRegistration);
            });

            //Act
            await _eventAppService.CancelRegistration(new EntityDto <Guid>(GetTestEvent().Id));

            //Assert
            UsingDbContext(context =>
            {
                var testEvent        = GetTestEvent(context);
                var testRegistration = context.EventRegistrations.FirstOrDefault(r => r.EventId == testEvent.Id && r.UserId == currentUserId);
                testRegistration.ShouldBeNull();
            });
        }