The GUID solutions did not work for me in VS 2022. Turns out all I needed to do was edit the project file and add the IsTestProject value:

<PropertyGroup>
  <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
  <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
  <ProjectGuid>{553487BF-FC0B-4FC5-B25B-C8C89A13F4ED}</ProjectGuid>
  <IsTestProject>true</IsTestProject>
  <OutputType>Library</OutputType>
  .
  .
  .
</PropertyGroup>