Test host process exited unexpectedly - Failed to queue test run: Unavle to start the agent process

All my unit tests started failing on VS2010. I don't know whether this was something to do with a VS2012 / .NET 4.5 install - I presume not as I'm convinced they were working after this.

Anyhow, they just stopped working.




























After 3 hours of investigation I found the way to get them working was to set
Test > Edit Test Settings > Hosts > Run tests in 32 bit or 64 bit process : Set to Run tests in 64 bit process on 64 bit machine

 

Note 32-bit debugging settings can be found in C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\QTAgent.exe.config. You can set the debug level to:

<switches>
      <!-- You must use integral values for "value".
           Use 0 for off, 1 for error, 2 for warn, 3 for info, and 4 for verbose. -->
      <add name="EqtTraceLevel" value="4" />
    </switches>

Use ProcMon to check that it is the QTAgent.exe that is being executed. VS2012 uses a different process.