The value for the MicrosoftNETPlatformLibrary property does not flow across project references. This typically means that test projects will run on a shared framework that is different from the app they are testing.

Example scenario:

src/WebApp.csproj

	<TargetFramework>netcoreapp2.1</TargetFramework>
    <PackageReference Include="Microsoft.AspNetCore.App" Version="2.1.1" />

test/WebAppTests.csproj

	<TargetFramework>netcoreapp2.1</TargetFramework>
    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="2.1.1" />
	<ProjectReference Include="../src/WebApp.csproj" />

• WebApp.runtimeconfig.json will contain "framework": { "name": "Microsoft.AspNetCore.App", "version": "2.1.1" }
• WebAppTests.runtimeconfig.json contains "framework": { "name": "Microsoft.NETCore.App", "version": "2.1.0" }

The result is that WebAppTests will run ASP.NET Core binaries out of NuGet packages, but the WebApp will execute off a shared runtime. Because of patch and minor runtime rollforward, this can mean the tests are executing something very different than the app.

cc @dsplaisted