Failed to negotiate protocol, waiting for response timed out

After upgrading to .Net 6 running dotnet test myproj.csproj failed with this error:

Failed to negotiate protocol, waiting for response timed out after 90 seconds. This may occur due to machine slowness, please set environment variable VSTEST_CONNECTION_TIMEOUT to increase timeout.

I found the solution here.

And in case that link disappears, basically you need to add to following to the test project:
<PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.9.1" />