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.

Answer 2

I found that I can run py.test with capture disabled, then use pdb.set_trace() as usual.

> py.test --capture=no
============================= test session starts ==============================
platform linux2 -- Python 2.5.2 -- pytest-1.3.3
test path 1: project/lib/test/test_facet.py

project/lib/test/test_facet.py ...> /home/jaraco/projects/project/lib/functions.py(158)do_something()
-> code_about_to_run('')
(Pdb)

Answer 3

The easiest way is using the py.test mechanism to create breakpoint

http://pytest.org/latest/usage.html#setting-a-breakpoint-aka-set-trace

import pytest
def test_function():
    ...
    pytest.set_trace()    # invoke PDB debugger and tracing

Or if you want pytest's debugger as a one-liner, change your import pdb; pdb.set_trace() into import pytest; pytest.set_trace()

Answer 4

I'm not familiar with py.test, put for unittest, you do the following. Maybe py.test is similar:

In your test module (mytestmodule.py):

if __name__ == "__main__":
    unittest.main(module="mytestmodule")

Then run the test with

python -m pdb mytestmodule.py

You will get an interactive pdb shell.

Looking at the docs, it looks like py.test has a --pdb command line option:

http://codespeak.net/py/dist/test/features.html