EventBusVerification.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 eventBusMock = new Mock<IEventBus>();
	eventBusMock
		.Setup(x=>x.Publish(It.IsAny<NewCustomerRegistered>()))
		.ReturnsAsync(Task.CompletedTask)
		.Verifiable();
	
	// Create the system under test with a stub and a mock	
	var useCase = new CustomerRegistrationUseCase(
		customerRepositoryStub, 
		eventBusMock.Object);
		
	await useCase.RegisterCustomer(testCustomerRegistrationRequest);
	
	eventBusMock.Verify(x=>x.Publish(It.IsAny<NewCustomerRegistered>()), Times.Once);
}