EventBusSpy.cs

[Fact]
public async Task ShouldPublishNotificationForSuccessfulRegistration()
{
	var customerRepositoryStub = CreateEmptyRepository();	
	
	// Notice, I don't really care about the values in the request 
	// because I am testing the collaboration with the event bus
    	var testCustomerRegistrationRequest = CreateTestRequest();
	var registrationEvent = default(NewCustomerRegistered);
	
	// Notice the use of a different kind of test double here - a SPY!
	var eventBusSpy = new Mock<IEventBus>();
	eventBusSpy
		.Setup(x=>x.Publish(It.IsAny<NewCustomerRegistered>()))
		.ReturnsAsync(Task.CompletedTask)
		.Callback<NewCustomerRegistered>(payload=> registrationEvent = payload);
	
	// Create the system under test with a stub and a spy
	var useCase = new CustomerRegistrationUseCase(
		customerRepositoryStub, 
		eventBusSpy.Object);
		
	await useCase.RegisterCustomer(testCustomerRegistrationRequest);
	
	registrationEvent.Should().NotBeNull();
	registrationEvent.Email.Should().Be(testCustomerRegistrationRequest.Email);	
	registrationEvent.FirstName.Should().Be(testCustomerRegistrationRequest.FirstName);
	registrationEvent.LastName.Should().Be(testCustomerRegistrationRequest.LastName);	
}