Python Testing with pytest

Combining pdb and tox

To debug the next test failure, we’re going to combine tox and pdb. For this to work, we have to make sure we can pass arguments through tox to pytest. This is done with tox’s {posargs} feature, which was discussed in ​Passing pytest Parameters Through tox​.

We’ve already got that set up in our tox.ini for Cards:

ch13/cards_proj/tox.ini

[tox]
envlist = py39, py310
isolated_build = True
skip_missing_interpreters = True

[testenv]
deps =
  pytest
  faker
  pytest-cov
commands = pytest --cov=cards --cov=tests --cov-fail-under=100 {posargs}

We’d like to run the Python 3.10 environment, and start the debugger at the test failure. We could run it once with -e py310, then use -e py310 -- --lf --trace ...