Simon Willison’s Weblog

Making PyPI's test suite 81% faster (via) Fantastic collection of tips from Alexis Challande on speeding up a Python CI workflow.

I've used pytest-xdist to run tests in parallel (across multiple cores) before, but the following tips were new to me:

• COVERAGE_CORE=sysmon pytest --cov=myproject tells coverage.py on Python 3.12 and higher to use the new sys.monitoring mechanism, which knocked their test execution time down from 58s to 27s.
• Setting testpaths = ["tests/"] in pytest.ini lets pytest skip scanning other folders when trying to find tests.
• python -X importtime ... shows a trace of exactly how long every package took to import. I could have done with this last week when I was trying to debug slow LLM startup time which turned out to be caused be heavy imports.