Had a problem today trying to run tests in Visual Studio 2008, where the test run would complete saying that all tests were not executed. A look in the test run details shoed the following error message;

“Code coverage collection error: The Visual Studio performance and coverage logging engine is already running on the computer. Therefore, the test run cannot continue. Close the pending performance or code coverage session and then rerun the tests.”

The solution is to shutdown the VSPerfMon.Exe process which gets left in memory when you debug a unit test and stop the debugger before the test finishes.

More information can be found here at Microsoft Connect.