The Slim server is started and stopped by FitNesse when you run a test, so there is no chance to attach to it and set breakpoints. To help debug your fixture code, you can use the GUI Slim server. This requires a change to the TEST_RUNNER definition.

!define TEST_RUNNER {c:\program files\fitsharp\RunnerW.exe}

When a Slim test is executed, this test runner opens a window and waits for you to press the Go button. You can attach your debugger to the test runner and set breakpoints in your fixture code. Pressing Go starts the test and pressing it again returns control to FitNesse.

You can also use this test runner to troubleshoot problems when a Slim test appears to hang. Any unhandled exceptions are caught and displayed in the test runner window.