We have host tests that test the project.json way dotnet test used to invoke the host in order to run tests.

See https://github.com/dotnet/core-setup/blob/6887ab556bc8302390782711dcdd75b75e769cf5/src/test/HostActivationTests/GivenThatICareAboutDotnetTestXunitScenarios.cs#L12

These tests rely on a bunch of old, no longer supported packages that enabled dotnet test on project.json based projects.

See
https://github.com/dotnet/core-setup/blob/3c952f2ca9f5d12057769ca6ce279ae3ee82ce50/src/test/Assets/TestProjects/StandaloneTestApp/StandaloneTestApp.csproj#L16-L17

We should investigate if we still need to maintain these tests, since this scenario isn't used by dotnet test anymore.

Note

The move to the 2.0.0 SDK brought this issue to light because PackageTargetFallback is deprecated in 2.0.0, and these tests rely on that behavior. See dotnet/core-setup#3320

@steveharter