Why is MS TestExplorer in VS2015RC not discovering Tests and showing test run result details?

The test explorer (MS-Test) kind of stopped working. It won’t discover any of my tests or sometimes only some of it. When I right click on my test and run it, the output window says “Run test finished: 1 run (time)”, but the test explorer would only display “Last Test Run Failed” (see screenshot), without information about which test or assert failed. I’ve tried restarting the VS, which I thought solved the issue once, but not currently. I’ve also tried build, rebuild, but I just can’t get it working again? Any idea what might help? All of this was working fine until early morning today...