Ok I was missing that after turning importlib back on, the issue returns, so in fact rewriting fails when importlib is turned on.

We need to verify what's up here

I suspect we are missing a bit where import lib will correctly fail for invalid module names, thus the assertions rewriter does as well, and then we incorrectly fall back to normal module loading

Most likely we try to find a test module inside a folder after not doing a sanity check on the filename, after that fails the normal import lib machinery takes over finding the module by path and working

I won't be able to verify before next week myself

I am having this issue as well. It seems that it only happens if I have my tests in a package:

root/
  my_module/
    __init__.py
    file.py
  tests/
    __init__.py
    test_main.py

If I remove __init__.py in the tests folder the assert rewriting works even in importlib mode. I should also note that my test files are valid module names, unlike the OP's.

I've had the same issue, the fix from @estyrke works, the test directories were erroneously packages, removing the __init__.pys fixes assertion rewriting.

Hitting the same problems, we keep out tests in the packages, but we need importlib to work-around issues with namespaced package. Keeping our tests inside the namespaced package, even by removing the __init__.py from the test folder breaks assertion rewriting when we upgraded from 8.0.2 to 8.2.0.

Moving the tests outside the namespace package fix it, but it's an unfortunate limitation.

Actually, it only keep happening with the config:

[pytest]
consider_namespace_packages = true

Without this, removing the __init__.py from a test folder fix it.