xUnit VS MediatR

Several well-known NuGet packages such as xUnit.net, FluentAssertions, StyleCop, Entity Framework Core, and others include by default a significant number of Roslyn analyzers. They help you adhere to the conventions and best practices of these libraries.

Most of my rules apply to document types, so let's build some tests for document types. We start by creating a new test class and a new test function and getting a list of all document types. This test is created using xUnit and FluentAssertions:

xUnit -> https://xunit.net/

.NET / xUnit / NUnit / MSTest

This library extends the traditional assertions provided by frameworks like MSTest, NUnit, or XUnit by offering a more extensive set of extension methods. Fluent Assertions supports a wide range of types like collections, strings, and objects and even allows for more advanced assertions like throwing exceptions.

You can verify the functionality of this validator by writing the following tests (using xUnit):

The git repo has other runners. AssemblyRunner appears to be the best fit for an already compiled tests project, but there is a runner that can be wrapped into an MSBuild task for example.

At this point you're going to see a familiar screen asking you to select a project. Here we're looking for a test project. By default, Visual Studio gives you access to 3 different testing frameworks based on your choice of project. These are MSTest, XUnit and NUnit. Ultimately, all 3 of these testing accomplish the same thing, and I've worked with all of them at various points in my career. The difference is mainly in exact syntax and documentation. Although, it's generally considered that MSTest is a little "older" than NUnit or XUnit, so I tend to see it less now. For the purposes of this demo, I'm going to go with NUnit:

xUnit unit tests tool

Use a testing framework: Utilize a testing framework like NUnit, xUnit, or MSTest to create, organize, and run your tests. These frameworks provide a consistent way to write tests, generate test reports, and integrate with continuous integration tools.

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.