Moq VS MediatR

In terms of mocking there are several frameworks you can use, but I've mainly relied on Moq and NSubstitute. Within this demo, I'm going to use NSubstitute as I've found it a little easier to use.

Or you just run into bullshit like https://github.com/Moq/moq4/issues/173

Now to the real benefit of DI: If you are testing a method in your application that calls the ReservationRepository.GetReservation() method, you can use a library like Moq to simply "mock" a class that uses the IReservationRepository interface and define the return result of the GetReservation() method. Pass the mocked class into the constructor of the class you are testing.

MOQ https://github.com/moq/moq4

Moq

Both projects use similar testing infrastructure. I write unit tests in C# using XUnit.net. I frequently use mock objects in testing, and MOQ is my tool of choice. I utilize continuous testing and coverage analysis through Rider. I do not have specific objectives for code coverage. When writing complicated algorithms, I frequently shoot for 100% coverage of the algorithm. I test simple properties inconsistently, and frequently do not test guard clauses.

🔗 Moq documentation | GitHub

But the reality is that I don't really write my tests with it. Toss on the MSTest attributes as needed of course. But all the testing code itself is FluentAssertions with a bit of Moq. (Though I find rarely need to use Moq/mocking anymore -- scandalous, I know.)

Moq tutorial

You probably noticed that .SetName() returns a Either. You may have come across Unit in libraries like MediatR or Language-Ext. It's a simple construct representing a type with only one possible value. We use it as a placeholder for operations that do not return a value but may return another state. In our example, .SetName() is a Command that does not return a value but may fail. Therefore, the monad Either carries two possible states: Right (without value) or Left (with an Error).

The widely used MediatR library[0] could be used to do that as well, just FYI.

[0]: https://github.com/jbogard/MediatR

Hope this GH issue shed some light on why injecting handler inside another handler is not good https://github.com/jbogard/MediatR/issues/400

From: https://github.com/jbogard/MediatR

I gave it a go and I was impressed how easy and fast it was to set it all up. Since I'm not a big fan of REPR pattern almost all my projects are using CQRS pattern with a help of MediatR ](https://github.com/jbogard/MediatR) I immediately started going over something similar that Fast Endpoints offer which is a command bus.

I'd use a dedicated event bus based on Reactive Extensions or MediatR to publish domain events from your domain services. This probably doesn't solve all your ViewModel update problems as is, maybe you need to revise the granularity (maybe you can have smaller ViewModels that refresh single property that exposes the Model) and lifespan (sometimes you can create a ViewModel, make it perform it's task and then discard it completely) of your ViewModels.

If you're finding yourself in a situation where you need to turn this behavior into a pattern because there are a lot of View Models that need to execute async business logic in response to some changes, I'd go with something like MediatR or Reactive Extensions. The idea is, again, that some other, probably business-level, component listens to changes in a decoupled way (that means it doesn't subscribe directly to your View Model, but to an event bus instead). View Model publishes change events to the event bus, and business-component reacts to these events by executing the business logic.

What people really want is to design the logic of an app independently from the component hierarchy. That means you need to store state somewhere other than the components and you need to dispatch events that are not attached to the component hierarchy. Also, a one way data flow has well known benefits as described by things like CQRS, RabbitMQ, and MediatR.