Seeking advice on making test more repeatable

[jaraco]

In the zipp project (part of CPython's stdlib), I've employed big O to test the complexity of zipp.CompleteDirs._implied_dirs. The tests fail intermittently, particularly on slower platforms (macOS, Windows, PyPy) but also even on Ubuntu in CI. The tests succeed fairly reliably locally. I'm fairly confident the implementation is linear, but sometimes the test reports linearithmic or cubic.

I'm wondering if you have any advice on how I might be able to tune the test to be more reliable. I'm wondering if garbage collection is at play, or maybe the problem is simply the variability from using shared compute resources.