Similar issue as this question (which does not have an answer), except we are using TFS 2013 Update 4. Our tests are written using NUnit and are configured to run through the build definition, which uses the default (not upgrade) template.
We just installed a full version of VS 2013 Premium on the build server (because prior tests were not being run at all). With that installed, the tests are run (if I did down into the log I can see them and the results, and if we force a failure the build appropriately fails) but the build summary says that 0/0 tests were run.
I followed the steps in the selected answer to this question, and it now shows the code coverage results, but still no dice on the actual tests or their results.
I also found this blog article that appears to be the same issue from TFS 2010. I have verified that all users have the View Test Runs permission set to allow, and I tried using a TFS administrator account just to be sure. Still no dice.
How do I make TFS show me what tests were run in the summary, and also in the Test Results window that the build summary links to?