title: Is it possible to unit test a class that makes P/Invoke calls?
body: <p>I want to wrap a piece of code that uses the Windows Impersonation API into a neat little helper class, and as usual, I'm looking for a way to go test-first. However, while WindowsIdentity is a managed class, the LogonUser call that is required to actually perform the logging in as another user is an unmanaged function in advapi32.dll. </p>
  
  <p>I think I can work around this by introducing an interface for my helper class to use and hiding the P/Invoke calls in an implementation, but testing that implementation will still be a problem. And you can imagine actually performing the impersonation in the test can be a bit problematic, given that the user would actually need to exist on the system.</p>