AsyncRequestHandler hides the Handle method

The AsyncRequestHandler class hides the Handle method, requiring tests to explicitly type the tested handler as IRequestHandler<TRequest>.

Consider following code:

public class MyRequest : IRequest {
}

public class MyHandler: AsyncRequestHandler<MyRequest> {
  protected override Task Handle(MyRequest request, CancellationToken cancellationToken) {
    // Do some work
  }
}

To test the code, one would expect following:

[Fact]
public async Task MyTest {
  var handler = new MyHandler();
  await handler.Handle(new MyRequest(), default);
  // Verify results
}

This results in compilation error CS0122: ‘MyHandler.Handle(MyRequest, CancellationToken)’ is inaccessible due to its protection level’

The workaround is to explicitly type the handler, making the code unnecessary bloated, especially with longer request and handler class names:

[Fact]
public async Task MyTest {
  IRequestHandler<MyRequest> handler = new MyHandler();
  await handler.Handle(new MyRequest(), default);
  // Verify results
}

[jbogard]

Honestly, I’d rather just remove these classes than anything else. I don’t use them anyway and they just seem to cause more problems than solve.

[cheesi]

Hello!

For me personally, the confusing thing about this is not the AsyncRequestHandler, it abstracts away the Unit.Value, which is a good thing imho, as for me the Unit.Value is the actual problem. I can understand, that it was most likely added to simplify things, but if you have never worked with MediatR before, you will find this thing very confusing.

Why is it named Unit.Value? Especially if it hasn’t any value? Wouldn’t NoValue be a better name? Also I would not remove AsyncRequestHandler. Adding a return Unit.Value to each command doesn’t provide any business value, it is an necessary implementation detail, that should be hidden way.

From my point of view there would be two good ways to go forward:

• Keep AsyncRequestHandler and make the Handle public, to make the unit testing easier without the workaround of setting the variable type to IRequestHandler<MyRequest>. @jbogard Do you have any problems with the execution time of your unit tests? We did a quick test setup on our side and saw the setup alone took about 160ms, which is too slow in our opinion (our “limit” is 100ms, which we try do achieve when it is possible)
• Another way I could see, would be using Default interface methods. Then the AsyncRequestHandler could be deprecated and the abstraction of it could be moved into the interface. I guess this would avoid any confusion between the interface and the abstract class.

What are your thoughts?