unit testing - Can I debug with python debugger when using py.test somehow?

Question

I am using py.test for unit testing my python program. I wish to debug my test code with the python debugger the normal way (by which I mean pdb.set_trace() in the code) but I can't make it work.

Putting pdb.set_trace() in the code doesn't work (raises IOError: reading from stdin while output is captured). I have also tried running py.test with the option --pdb but that doesn't seem to do the trick if I want to explore what happens before my assertion. It breaks when an assertion fails, and moving on from that line means terminating the program.

Does anyone know a way to get debugging, or is debugging and py.test just not meant to be together?

Answer 1

it's real simple: put an assert 0 where you want to start debugging in your code and run your tests with:

py.test --pdb 

done :)

Alternatively, if you are using pytest-2.0.1 or above, there also is the pytest.set_trace() helper which you can put anywhere in your test code. Here are the docs. It will take care to internally disable capturing before sending you to the pdb debugger command-line.