Strategy to ensure assemblies are loaded during unit testing in ADO and are counted against testing metrics

Question

So I ran into a bit of an embarrassing situation recently where my test coverage via pipeline was fantastic but a bug came out, and root cause analysis found that it was in a very small project/dll/library that wasn't referenced by unit tests at all so ADO didn't actually list it in the assemblies tested against Some 200 lines of untested code. I think the new project got put in during a crunch as part of a very large commit, but somehow we managed to unit test around it. Obviously not ideal -- I'd like to get some sort of warning if a project that we build isn't unit tested.

I'm considering doing some sort of hinky "Load every DLL who's name starts with [prefix] scheme as part of the test project, but that's custom and dumb and it seems like there has got to be a better way. I'm using MSTest for my test framework, so if there's something built in there that would be ideal.