Tuesday, 28 September 2010

Why you can’t assert a return type of an MVC Controller Action using reflection!

I recently asked this question on Stack Overflow.  I was using reflection and MethodInfo to confirm that a controller contained an action with the required method parameters.  If one was found, this would then allow my code to unit test that the correct Action Filter Attributes were being assigned to the controller action (so a particular action could only respond to an HTTP GET or POST as an example).  

This was all working fantastically well but I made the mistake of trying a unit test too far and was surprised by the outcome.  I was attempting to assert/validate the return type was of the desired type (e.g. ActionResult or JSONResult) but my assertion was failing.  In the debug watch window I could see the return parameter was of the desired type but it was wrapped up inside a RuntimeType.  No amount of fiddling / casting would get the test to pass.  Another SO user helpfully pointed out that an MVC action might actually return RedirectToRouteResult, etc. so the wrapping was a requirement of the call – it was working as intended.

Thinking this through to it’s conclusion my original test was flawed, even if it was possible there is no need to test the return type of the reflected method info.   Only when I am testing actual calls to the controller am I interested in what the returned type is and what it contains!

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