An exception occurred while invoking executor 'executor://mstestadapter/v1': Object reference not set to an instance of an object

Question

We are using Visual Studio 2012 and Team Foundation Server 2010 in our project. Since, we are using Microsoft Fakes, we could have not used the started Test functionality of our Team Build 2010, I have created a build activity which invokes VSTest.Console.exe passing the test assemblies. This approach has been working well for us. However, after a recent check-in we are getting the following error when executing Vstest.console.exe

Error: An exception occurred while invoking executor 'executor://mstestadapter/v1': Object reference not set to an instance of an object.

I copied the binary files to my local machine and was able to get the error again. Interestingly, we run a dev build before check-in which runs the same vstest.console.exe with the same parameters and that works correctly. I have got two folders on my machine, for one the call works fine and for other it doesn't. The compiled assemblies look same size and there aren't much differences to suggest.

I tried using Process Monitor but couldn't find anything obvious other than that the process returns with an exit code 1. Does anybody know much about this error? Is there any way I can find out more information from my test run?

Regards,

Hamid

Answer 1

We got to the bottom of the problem. We are using Entity Framework 5.0 and we also have a situation where some of our test assemblies are targeting .Net 4.0 and some are targeting .Net 4.5.

When we are trying to run the tests such that assemblies targeting different versions of .Net framework and using Entity Framework 5.0 are run in the same Test (vstest.console.exe) process, we get this error.

I think this has to do with the way Entity Framework 5.0 ships with two versions (net40 and net45). Once one version of the library is loaded in the process, the other version cannot be loaded and this caused the error.