Tests need extra work to enable switches in .NET Framework

[dougbu]

The app.config approaches described in README.md don't work when testing with .NET Framework. While dotnet test --framework netcoreapp2.0 correctly uses settings from {TestAssemblyName}.runtimeconfig.json, the same is not true of dotnet test --framework net462 and settings from {TestAssemblyName}.dll.config.

I ended up changing $env:UserProfile\.dotnet\x64\sdk\2.1.0-preview1-007042\TestHost\testhost.x86.exe.config to add the setting and get it recognized in full-framework test runs. Feels like an ugly hack…

I suggest an update to README.md. Might also be worth checking around for other approaches.