Sometimes you need to dump something that is in the CFC you are testing. The debug() method is only accessible from your test cfc, so usually people end up writing temp variables to the request scope and come up with a homemade solution to this (see recent thread in testing on slack channel).
MXUnit had a request.debug() feature: https://github.com/mxunit/mxunit/wiki/Using-request.debug() I don't know if it needs to be implemented exactly the same way (I never used this, and didn't know about it until someone mentioned it in slack).
We have created a request.testbox struct that will contain all the output utilities that TestBox Provides:
Send output to the console
Send output to the TestBox reporter debugger
Clear the debugger
Send output to the ColdFusion output buffer
Same as print() but adding a <br> separator
This way in your code you can add them for better debugging, especially when testing async code: