WebApplicationFactory and *.deps.json files?

[kimbell]

I've been using the WebApplicationFactory<> since it arrived without any problems. As we have built up experience with the new platform, we are trying to build libraries that set things up for our infrastructure. One of the areas we are working on is testing.

We have a standard SDK project (Microsoft.NET.Sdk) that contains a base class for setting this up for our use. public abstract class BaseTestContext<TStartup> : WebApplicationFactory<TStartup> where TStartup : class

In my project I also have some sample projects (Microsoft.NET.Sdk.Web). And I have created matching test projects for these.
In these test projects, I'm using a derived class from BaseTestContext. The derived class is in the test assembly. The startup class being references is in the sample project.

When I try to run the test, I get an error.
Can't find'C:\src\MyProject\test\MyProject.Sample,Tests\bin\Debug\netcoreapp3.1\MyProject.Sample.deps.json'. This file is required for functional tests to run properly. There should be a copy of the file on your source project bin folder. If that is not the case, make sure that the property PreserveCompilationContext is set to true on your project file. E.g 'true'. For functional tests to work they need to either run from the build output folder or the MyProject.Sample.deps.json file from your application's output directory must be copied to the folder where the tests are running on. A common cause for this error is having shadow copying enabled when the tests run

My output folder contains MyProject.Sample,Tests.deps.json, but not MyProject.Sample.deps.json

In another project that contains multiple assemblies in the same solution, I have multiple deps files.

What controls which deps.json files get copied? I tried adding the PreserveCompilationContext all over the place, but it didn't seem to make any difference. Is this controlled by SDK project type? some other magical MSBuild properties that should be set/not set?

Repro: https://github.com/kimbell/depsTestingIssue

[kimbell]

I managed to resolve this by adding
<PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="3.1.9" />
to the problematic projects. This has MSBuild targets that copies things correctly.
I had the reference in the my common testing project, but this doesn't get applied transitively.