Debug.WriteLine() happening twice when running tests

Question

I have an odd problem in VS2008 running unit tests. When I run the unit test using either Resharper or TestDriven, in either normal or Debug mode, the Debug.WriteLine("foo") lines are being carried out twice: ie. in the Output window of VS I can see each line written twice.

If I step through the test, however, each line seems to be carried out once as expected. Anyone know what is going on here? Thanks!

Answer 1

IIRC the Studio's Output window displays not only STDOUT and STDERR but also trace messages. A proper test runner might set up a tracing additionally to writing to STDOUT, something which doesn't happen if you step into the test manually.