What are we doing?

• we have a processing pipeline built using MediatR IPipelineBehaviour<TRequest, TRespons>
• The typical pattern:
  • Command/Query
  • dispatch using IMediator.Send(thing)
  • PiplineBehaviour 1 to n (can forward to next behaviour or short circuit and send a response)
  • Handler - generates a response

Why MediatR?

• composability
• avoid rebuilding the same logic for an API vs a daemon. As we do not tie ourselves to a hosting platform (e.g. if we were using ASP.NET filters, we cannot use them on a daemon )

The testing issue

the signature of a PipelineBehaviour Handle is so:

public async Task<TResponse> Handle(SomeContext context, CancellationToken cancellationToken, RequestHandlerDelegate<TRequest> next)

Scenario

• We want to test that given some workflow, if the behaviour executes successfully, we should call the next delegate
• We mock the delegate using NSubstitute

var stubNext = Substitute.For<RequestHandlerDelegate<TRequest>>();

// test - Arrange, Act 

// Assert next was called. We're using Shouldly as our assertion library

stubNext.Received(1).Invoke();