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atexit registered functions that print to stdout break test discovery #6581
Description
When exit handlers that print to standard out are registered using the atexit module, pytest test discovery fails.
Environment data
- VS Code version: 1.36.1
- Extension version (available under the Extensions sidebar): 2019.6.24221
- OS and version: Ubuntu Linux 18.04.2
- Python version (& distribution if applicable, e.g. Anaconda): Python 3.7.4
- Type of virtual environment used (N/A | venv | virtualenv | conda | ...): virtualenv
- Relevant/affected Python packages and their versions: pytest
- Jedi or Language Server? (i.e. what is
"python.jediEnabled"set to; more info How to update the language server to the latest stable version #3977): Language Server
Expected behaviour
I would expect the relevant tests to be discovered.
Actual behaviour
Test discovery fails because extra text is appended to whatever output is used to store the JSON description of the discovered tests, which subsequently causes a SyntaxError when parsing.
Steps to reproduce:
Allow test discovery to run on the minimal demonstration repository here: https://github.com/joel-wright/pytest-discovery-atexit
Logs
Output for Python Test Log:
python /home/jjw/.vscode/extensions/ms-python.python-2019.6.24221/pythonFiles/testing_tools/run_adapter.py discover pytest -- -s --cache-clear
Test Discovery failed:
SyntaxError: Unexpected token I in JSON at position 436
Activity
ericsnowcurrently commentedon Jul 15, 2019
That is definitely a function of how our test discovery tooling works. We capture stdout while pytest discovery runs (and only show it on failure) and then write the discovery results to stdout. The best we could do for now is to clear all atexit handlers before the discovery tool finishes. However, doing so would require a bit of a hack (monkey-patching
atexit.register()), so it might not be worth it.FWIW, we are looking into an alternative approach that would not break with your atexit handler, but that would not be happening any time soon.
joel-wright commentedon Jul 16, 2019
I love the sound of the alternative approach (I discovered this in a relatively large project where test discovery takes multiple minutes).
luabud commentedon Sep 17, 2019
Closing in favour of #6594.