Pytest gives exit code 127

I have a step in a GitHub Actions CI job that has a single invocation of pytest, like so:

    - name: Run test suite using pytest
      env:
        # For test_cli.test_dl; see code in message_ix.cli.dl
        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
      working-directory: message_ix
      run: |
        pytest message_ix -m "not nightly" -rA --verbose --cov-report=xml --color=yes
      shell: bash

Pytest runs successfully, and all tests pass (see here):

…
XFAIL message_ix/tests/test_core.py::test_add_horizon[args7-kwargs7-None]
XFAIL message_ix/tests/test_core.py::test_add_horizon[args8-kwargs8-None]
==== 113 passed, 2 deselected, 5 xfailed, 4 warnings in 509.99s (0:08:29) =====

However, the overall CI step and job fails, because pytest is apparently returning exit code 127—which, according to the docs, should never happen.

Further information:

• This occurs only on Windows Server 2019 job runners; not on (Ubuntu) Linux or macOS.
• I experimented with modifying the line like so:

      run: |
        pytest message_ix -m "not nightly" -rA --verbose --cov-report=xml --color=yes || echo "Spurious exit code $? from pytest"
  

  …and indeed the message “Spurious exit code 127 from pytest” is printed.
• In bash, exit code 127 is for a command not found; but the only command here is pytest, which is clearly found, because it runs.
• I wonder if this may be something in the tests that I am running that somehow “leaks through” pytest; but I am at a total loss as to how to identify and debug that.

Output of `pip list`, including pytest

From https://github.com/iiasa/message_ix/pull/453/checks?check_run_id=2253546265#step:17

Package                       Version
----------------------------- --------------------
alabaster                     0.7.12
argon2-cffi                   20.1.0
async-generator               1.10
asyncssh                      2.5.0
atomicwrites                  1.4.0
attrs                         20.3.0
Babel                         2.9.0
backcall                      0.2.0
bleach                        3.3.0
certifi                       2020.12.5
cffi                          1.14.5
chardet                       4.0.0
click                         7.1.2
cloudpickle                   1.6.0
colorama                      0.4.4
coverage                      5.5
cryptography                  3.4.7
cycler                        0.10.0
dask                          2021.3.1
decorator                     5.0.1
defusedxml                    0.7.1
descartes                     1.1.0
docutils                      0.16
entrypoints                   0.3
et-xmlfile                    1.0.1
fsspec                        0.8.7
genno                         1.3.0
iam-units                     2021.3.22
idna                          2.10
imagesize                     1.2.0
iniconfig                     1.1.1
ipykernel                     5.5.3
ipython                       7.22.0
ipython-genutils              0.2.0
ipywidgets                    7.6.3
ixmp                          3.2.1.dev71+g33404fd
jedi                          0.18.0
Jinja2                        2.11.3
JPype1                        1.2.1
jsonschema                    3.2.0
jupyter                       1.0.0
jupyter-client                6.1.12
jupyter-console               6.4.0
jupyter-core                  4.7.1
jupyterlab-pygments           0.1.2
jupyterlab-widgets            1.0.0
kiwisolver                    1.3.1
latexcodec                    2.0.1
llvmlite                      0.36.0
locket                        0.2.1
MarkupSafe                    1.1.1
matplotlib                    3.4.1
message-ix                    3.2.1.dev49+gbe45b14
mistune                       0.8.4
mizani                        0.7.3
nbclient                      0.5.3
nbconvert                     6.0.7
nbformat                      5.1.3
nest-asyncio                  1.5.1
notebook                      6.3.0
numba                         0.53.1
numpy                         1.20.2
numpydoc                      1.1.0
openpyxl                      3.0.7
packaging                     20.9
palettable                    3.3.0
pandas                        1.2.3
pandocfilters                 1.4.3
parso                         0.8.2
partd                         1.1.0
patsy                         0.5.1
pickleshare                   0.7.5
Pillow                        8.2.0
Pint                          0.17
pip                           21.0.1
plotly                        4.14.3
plotnine                      0.8.0
pluggy                        0.13.1
prometheus-client             0.9.0
prompt-toolkit                3.0.18
py                            1.10.0
pyam-iamc                     0.10.0
pybtex                        0.24.0
pybtex-docutils               1.0.0
pycparser                     2.20
Pygments                      2.8.1
pyparsing                     2.4.7
pyrsistent                    0.17.3
pytest                        6.2.2
pytest-cov                    2.11.1
python-dateutil               2.8.1
pytz                          2021.1
pywin32                       300
pywinpty                      0.5.7
PyYAML                        5.4.1
pyzmq                         22.0.3
qtconsole                     5.0.3
QtPy                          1.9.0
requests                      2.25.1
retrying                      1.3.3
scipy                         1.6.2
seaborn                       0.11.1
Send2Trash                    1.5.0
setuptools                    49.2.1
setuptools-scm                6.0.1
six                           1.15.0
snowballstemmer               2.1.0
sparse                        0.12.0
Sphinx                        3.5.3
sphinx-rtd-theme              0.5.1
sphinxcontrib-applehelp       1.0.2
sphinxcontrib-bibtex          2.2.0
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
statsmodels                   0.12.2
terminado                     0.9.4
testpath                      0.4.4
toml                          0.10.2
toolz                         0.11.1
tornado                       6.1
traitlets                     5.0.5
urllib3                       1.26.4
wcwidth                       0.2.5
webencodings                  0.5.1
wheel                         0.36.2
widgetsnbextension            3.5.1
xarray                        0.17.0
xlrd                          1.2.0

[asottile]

it’s probably not atexit – it’s probably when the interpreter runs destructors of globals while tearing down the process

does this reproduce when you run locally on windows? there’s free VMs you can try out at https://modern.ie provided by microsoft

[asottile]

maybe try debugging where the exit is coming from?

import sys
import pytest
import traceback
try:
    pytest.main(sys.argv[1:])
except BaseException:
    traceback.print_exc()
    raise