Visual Studio 15.8.1 not running MS unit tests

Question

When I updated Visual Studio to the latest version, 1 of my test projects stopped running tests and outputted this message:

Test project {} does not reference any .NET N

Answer 1

My reputation score does not currently allow me to add this as a comment to the accepted answer. For reference, I've appended version numbers to the nuget packages referenced in csharpsql's answer:

MSTest.TestAdapter v1.3.2
MSTest.TestFramework v1.3.2
Microsoft.NET.Test.Sdk v15.9.0