I had an issue with ReSharper where it was running my unit tests sometimes and not always. I am using Resharper 9 and VS2013. It was working fine, but suddenly stopped. ReSharper’s unit test window stayed grey, the spinning icon endlessly.

Tried things like restarting Visual Studio, rebuilding solution, running Visual Studio in administration mode and even restarting my computer but I was still not closer to getting my unit tests running.

Eventually I cleared ReSharper cache using ReSharper’s options (Resharper > Options > Environment > General > Clear Cache), and after clearing ReSharper’s cache and restarting Visual Studio I was able to run my unit tests once again.