It seems that if pytest is run in a development directory, it can create files in site-packages/.../__pycache__ which can cause modules to continue getting "imported" even when they are uninstalled.

Many packages use import X as proof of an X package is installed and available.

If you:

1. Install an optional package
2. Run pytest
3. Uninstall the optional package

It can leave your environment in a broken state.

Your input on "why" this is happening would be appreciated.

I wrote out my explanation and reproducer conda-forge/cupy-feedstock#188 (comment)

• a detailed description of the bug or problem you are having
• output of pip list from the virtual environment you are using
• pytest and operating system versions
• minimal example if possible