Can I force MSTest to use a new process for each test run?

Question

We're using the VS 2010 test runner (MSTest) for automated functional testing. When we run tests from Visual Studio, VS creates a process called QTAgent32.exe, and it runs the tests in that process.

We've found that when we do multiple test runs, MSTest will reuse the same QTAgent32 process - the process ID does not change. This is a problem for us, since the code we're testing is P/Invoking to an unmanaged DLL. The DLL needs to be initialized only once during the lifetime of the process. We have an [AssemblyInitialize] method, but that executes once per test run. If we perform multiple test runs, it will execute more than once in the same process.

Every time we do a test run, MSTest creates a new appdomain; but these appdomains are all in the same process.

So I'm wondering: is there a way to tell the Visual Studio test runner to use a new process every time we run tests? I looked at the ".testsettings" configuration but didn't see anything relevant.

Answer 1

dont know how far you want to go with it, but one solution could be to create your unit test host

http://technet.microsoft.com/fr-fr/query/bb166558

this link shows how to create adapters, also you could then launch a new process for evertest, create a piped communication and tear it down after the test.

I know MS itself uses a different host for running tests under moles

http://research.microsoft.com/en-us/projects/pex/molestutorial.pdf

Answer 2

I was able to get this working after reading Wiktor's comment about FreeLibrary().

I used this class created by Mike Stall, which provides wrappers around LoadLibrary, GetProcAddress, and FreeLibrary. That way, I can load the library once in each test run, call the necessary methods, and then free the library at the end of the test run.

Mike Stall's code uses Marshal.GetDelegateForFunctionPointer , which converts an unmanaged function pointer to a managed delegate type.

I had to replace the [DllImport] extern declarations with declarations for delegate types. So I converted this:

[DllImport("asesignal.dll")]
public static extern bool ASESDK_Initialize(string licenseCode);

to this:

public delegate bool ASESDK_Initialize(string licenseCode);

Mike Stall's code contained examples with generic delegates (Action<T> etc.). But I couldn't get that working, so I created my own delegate types.

I can load the DLL dynamically like this:

_ht = new UnmanagedLibrary(@"c:\windows\system32\asesignal.dll");

To call a function, I do this:

var function = _ht.GetUnmanagedFunction<ASESDK_Initialize>("ASESDK_Initialize");
function(licenseCode);

Thanks Wiktor and np-hard for your help!

Answer 3

VS 2013 and forward now has a setting for this under Test > Test Settings > Keep Test Execution Engine Running. Unchecking this selection will start up a new engine each run.