Move shared unit test code to a shared assembly

[GangWang01]

Fixes #8364

Context

As the issue mentions /src/Shared/UnitTests shares functionality in unit tests via shared code files. Actually they should be moved to /src/UnitTests.Shared/Microsoft.Build.UnitTests.Shared.csproj

Changes Made

Assemble share code files with common functions in unit tests from /src/Shared/UnitTests into /src/UnitTests.Shared/Microsoft.Build.UnitTests.Shared.csproj

Testing

Notes

[GangWang01]

There are also some code files with tests shared among multiple projects. For example, src/Shared/UnitTests/ErrorUtilities_Tests.cs is shared in the following test projects.

• src\Build.UnitTests\Microsoft.Build.Engine.UnitTests.csproj
• src\Tasks.UnitTests\Microsoft.Build.Tasks.UnitTests.csproj
• src\Utilities.UnitTests\Microsoft.Build.Utilities.UnitTests.csproj

Is there any difference running the same set of tests in such a shared test code file multiple times in different projects?

[rainersigwald]

There are also some code files with tests shared among multiple projects. For example, src/Shared/UnitTests/ErrorUtilities_Tests.cs is shared in the following test projects.

• src\Build.UnitTests\Microsoft.Build.Engine.UnitTests.csproj
• src\Tasks.UnitTests\Microsoft.Build.Tasks.UnitTests.csproj
• src\Utilities.UnitTests\Microsoft.Build.Utilities.UnitTests.csproj

Is there any difference running the same set of tests in such a shared test code file multiple times in different projects?

I think this is because the code under test src/Shared/ErrorUtilities.cs is compiled into several product assemblies, so it makes sense to test each of those assemblies. So let's leave it for now. However, as we move that stuff into Framework, we can single-instance the tests.

[rainersigwald]

Love it!

[AR-May]

LGTM