I don't know why, but uninstalling the Office Tools extension seems to fix it.
Edit: I tried to reproduce this error, I ran the VS2013.5 update and clicked the fix. The update took +5 hours, thought he was stuck. So I canceled it, canceled the cancellation. So I finished this process. Now I started a visual studio, and TEST is missing, basically my installation of a visual studio is corrupted, I think.
Edit: Found the culprit, it was Microsoft Intune Endpoint Protection installed on my computer. He basically scanned everything, and when the visual studio was updated and the files were written to disk, something went wrong and messed up my installation. I disabled it by excluding C:\* from the scan and performing VS2013.5 update and clicking repair. Now everything is all right.
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