How best to unit test a ServiceStack service that uses IServiceGateway to call other internal services - unit-testing

Question

I've been following the guidelines here - https://docs.servicestack.net/testing
I'm trying to do unit testing rather than integration, just to cut down the level of mocking and other complexities.
Some of my services call some of my other services, via the recommended IServiceGateway API, e.g. Gateway.Send(MyRequest).
However when running tests i'm getting System.NotImplementedException: 'Unable to resolve service 'GetMyContentRequest''.
I've used container.RegisterAutoWired() which is the service that handles this request.
I'm not sure where to go next. I really don't want to have to start again setting up an integration test pattern.

Answer 1

You're likely going to continually run into issues if you try to execute Service Integrations as unit tests instead of Integration tests which would start in a verified valid state.
But for Gateway Requests, they're executed using an IServiceGateway which you can choose to override by implementing GetServiceGateway() in your custom AppHost with a custom implementation, or by registering an IServiceGatewayFactory or IServiceGateway in your IOC, here's the default implementation:
public virtual IServiceGateway GetServiceGateway(IRequest req)
{
if (req == null)
throw new ArgumentNullException(nameof(req));
var factory = Container.TryResolve<IServiceGatewayFactory>();
return factory != null ? factory.GetServiceGateway(req)
: Container.TryResolve<IServiceGateway>()
?? new InProcessServiceGateway(req);
}

Answer 2

Based on the discussion in the answer by #mythz, this is my solution:
Use case like OP: Test the "main" service, and mock the "sub service", and like OP I'd want to do that with Unit test (so BasicAppHost), because it's quicker, and I believe it is easier to mock services that way (side note: for AppHost based integration test, SS will scan assemblies for (real) Services, so how to mock? Unregister from "container" and replace w. mock?).
Anyway, for the unit test:
My "main" service is using another service, via the IServiceGateway (which is the officially recommended way):
public MainDtoResponse Get(MainDto request) {
// do some stuff
var subResponse = Gateway.Send(new SubDto { /* params */ });
// do some stuff with subResponse
}
In my test setup:
appHost = new BasicAppHost().Init();
var mockGateway = new Mock<IServiceGateway>(); // using Moq
mockGateway.Setup(x => x.Send<SubDtoResponse>(It.IsAny<SubDto>()))
.Returns(new SubDtoResponse { /* ... */ });
container.Register(mockGateway.Object);
So the IServiceGateway must be mocked, and then the Send method is the important one. What I was doing wrong was to mock the service, when I should have mocked the Gateway.
Then call the main service (under test) in the normal fashion for a Unit Test, like in the docs:
var s = appHost.Container.Resolve<MainService>(); // must be populated in DI manually earlier in code
s.Get(new MainDto { /* ... */ })
PS: The mockGateway.Setup can be used inside each test, not necessarily in the OneTimeSetUp.