Question: How to properly leverage the DistributedApplicationTestingBuilder.CreateAsync<TEntryPoint>()

[BenjaminCharlton]

I'm working on a new Aspire feature that I hope will be accepted as a Pull Request by the Aspire team.
(See an explanation and my progress here, if interested: #4785)

However, I'm struggling with my unit tests. I'm trying to use the CreateAsync method of the DistributedApplicationTestingBuilder to get a mock distributed application

var distributedApplicationBuilder = await DistributedApplicationTestingBuilder.CreateAsync<BlazorFluentUI_AppHost>();

It was working fine in my own test project in my own solution, where I was passing the type of a recently created AppHost project as the value of T. However, when I copied my unit tests into the Aspire solution (\tests\Aspire.Hosting.Tests) some of them started failing. I tried various values of T, including TestingAppHost1_AppHost (which is a distributed application host project already referenced by the Aspire.Hosting.Tests project.

In all cases above, I got the message:

System.InvalidOperationException : The entry point exited without building a DistributedApplication.

Please could you tell me what class I can use to bootstrap DistributedApplicationTestingBuilder to use in my unit tests?

Thanks for your help!

Benjamin

[davidfowl]

Can you share a sample?

[BenjaminCharlton]

Hi @davidfowl! Happy New Year! Sure, how about this test in the file linked here. The method named BlazorResourceBuilderExtensionsTests.AddWebAssemblyClient_WithoutConfigure_InvokesDefaultConfiguration

The first line of that test is:

 var distributedApplicationBuilder = await DistributedApplicationTestingBuilder.CreateAsync<Projects.Aspire4Wasm_DummyApp_AppHost>();

And it throws:

System.InvalidOperationException : The entry point exited without building a DistributedApplication.

The type that I pass into the type argument TEntryPoint is the app host of an unedited Aspire template app Projects.Aspire4Wasm_DummyApp_AppHost, which is referenced by the unit test project.

Could you let me know if that's how DistributedApplicationTestingBuilder was supposed to be used, please? I wondered what I'd done to make it fail. I also wondered if linking a complete dummy app was unnecessary, and maybe there was a lightweight class that could be used as the TEntryPoint for testing purposes?

[davidfowl]

var distributedApplicationBuilder = await DistributedApplicationTestingBuilder.CreateAsync<Projects.Aspire4Wasm_DummyApp_AppHost>();

The type that I pass into the type argument TEntryPoint is the app host of an unedited Aspire template app Projects.Aspire4Wasm_DummyApp_AppHost, which is referenced by the unit test project.

Could you let me know if that's not how DistributedApplicationTestingBuilder was supposed to be used, please?

No that's not correct. The entry point must be a type in the apphost's assembly (usually the Program type). The DistributedApplicationTestingBuilder runs the apphost project. The type is used to find the entryponit assembly. I know Projects.XX looks like it should work, but that's the generated class used by the apphost to avoid hard coding project paths.

[BenjaminCharlton]

Thanks @davidfowl that got all those tests passing! Much appreciate the help.