Flag to simply not catch exceptions at all

Problem

Using pytest 5.4.2 I don’t see a flag that simply tells pytest to not catch any exceptions. So on the first test that raises and unhandled exception, pytest itself would exit with that exception.

Background

I’m trying to debug tests with vscode’s Python extension’s debugpy debugger. It does not support --pdb or --pdbcls. So there is no obvious way to get it to break on an exception. If pytest would simply not catch any exceptions, then any debugger could break on that unhandled exception. In this case I’m running a single test.

I’m sure it’s been a design goal of pytest that it itself never “crashes” but in this case it would make it easy to debug pyttest tests with any debugger.

References

vscode/python/debug/py is working on a solution: https://github.com/microsoft/debugpy/issues/275

• a detailed description of the bug or suggestion
• output of pip list from the virtual environment you are using
• pytest and operating system versions

Environment

pytest 5.4.2 macOS 10.15.3 conda

Package Version

---

alabaster 0.7.12
appdirs 1.4.4
appnope 0.1.0
asciitree 0.3.3
astroid 2.4.1
attrs 19.3.0
Babel 2.8.0
backcall 0.1.0
bleach 3.1.5
cachey 0.2.1
certifi 2020.4.5.1
chardet 3.0.4
cycler 0.10.0
dask 2.17.2
decorator 4.4.2
defusedxml 0.6.0
docutils 0.16
entrypoints 0.3
fasteners 0.15
flake8 3.8.2
freetype-py 2.1.0.post1
fsspec 0.7.4
future 0.18.2
graphviz 0.14
HeapDict 1.0.1
idna 2.9
imageio 2.8.0
imagesize 1.2.0
ipykernel 5.3.0
ipython 7.14.0
ipython-genutils 0.2.0
ipywidgets 7.5.1
isort 4.3.21
jedi 0.17.0
Jinja2 2.11.2
jsonschema 3.2.0
jupyter 1.0.0
jupyter-client 6.1.3
jupyter-console 6.1.0
jupyter-core 4.6.3
kiwisolver 1.2.0
lazy-object-proxy 1.4.3
MarkupSafe 1.1.1
matplotlib 3.2.1
mccabe 0.6.1
mistune 0.8.4
monotonic 1.5
more-itertools 8.3.0
mypy 0.780
mypy-extensions 0.4.3
napari 0.3.2
napari-plugin-engine 0.1.5
napari-svg 0.1.3
nbconvert 5.6.1
nbformat 5.0.6
networkx 2.4
notebook 6.0.3
numcodecs 0.6.4
numpy 1.18.4
numpydoc 1.0.0
packaging 20.4
pandas 1.0.4
pandocfilters 1.4.2
parso 0.7.0
pexpect 4.8.0
pickleshare 0.7.5
Pillow 7.1.2
pip 20.0.2
pluggy 0.13.1
pooch 1.1.1
prometheus-client 0.8.0
prompt-toolkit 3.0.5
psutil 5.7.0
ptyprocess 0.6.0
py 1.8.1
pycodestyle 2.6.0
pyflakes 2.2.0
Pygments 2.6.1
pylint 2.5.2
PyOpenGL 3.1.5
pyparsing 2.4.7
PyQt5 5.14.2
PyQt5-sip 12.7.2
pyrsistent 0.16.0
pytest 5.4.2
pytest-faulthandler 2.0.1
pytest-ordering 0.6
pytest-qt 3.3.0
pytest-timeout 1.4.1
python-dateutil 2.8.1
pytz 2020.1
PyWavelets 1.1.1
PyYAML 5.3.1
pyzmq 19.0.1
qtconsole 4.7.4
QtPy 1.9.0
requests 2.23.0
scikit-image 0.17.2
scipy 1.4.1
Send2Trash 1.5.0
setuptools 46.4.0.post20200518 shiboken2 5.15.0
six 1.15.0
snowballstemmer 2.0.0
Sphinx 3.0.4
sphinxcontrib-applehelp 1.0.2
sphinxcontrib-devhelp 1.0.2
sphinxcontrib-htmlhelp 1.0.3
sphinxcontrib-jsmath 1.0.1
sphinxcontrib-qthelp 1.0.3
sphinxcontrib-serializinghtml 1.1.4
terminado 0.8.3
testpath 0.4.4
tifffile 2020.5.25
toml 0.10.1
toolz 0.10.0
torch 1.5.0
torchvision 0.6.0
tornado 6.0.4
traitlets 4.3.3
typed-ast 1.4.1
typing-extensions 3.7.4.2
urllib3 1.25.9
vispy 0.6.4
wcwidth 0.1.9
webencodings 0.5.1
wheel 0.34.2
widgetsnbextension 3.5.1
wrapt 1.12.1
xarray 0.15.1
zarr 2.4.0

[pwinston]

Your two hookimpl work great for me. I’ve wrapped then in a env var. So I can run pytest normally or when debugging I can set that var, and then the debugger breaks in the right spot.

I think there should be a pytest flag that does this. I know --pdb and --pdbcls and sys.breakpointhook are all trying to address this more elegantly. But none of the three seem to work with vscode yet, at least for exceptions. Simply letting pytest crash works with any debugger past, present and future. I can see why pytest would be uncomfortable with this idea, though, but it really hits the spot in this case.

This works 100% for me and maybe Google will send other people here. Thanks for such a quick and helpful response. This was the thread me asking vscode Python people how to make this work: https://github.com/microsoft/debugpy/issues/275#issuecomment-648984822. They had some ideas but no real solution today. This stack overflow has the answer now.

[bluetech]

Does vscode set sys.breakpointhook?

---

You can cause pytest to crash with a plugin such as this, but don’t do that 😃

import pytest

@pytest.hookimpl(tryfirst=True)
def pytest_exception_interact(call):
    raise call.excinfo.value

@pytest.hookimpl(tryfirst=True)
def pytest_internalerror(excinfo):
    raise excinfo.value