It seems that other test is causing video ones to fail:

Also, order don't seem to affect:

test_io_opt seems to be the culprit for the failure of the tests, I don't know what is the intent of that test

Edit: The error occurs when set_video_backend('video_reader') is called. If set_video_backend('pyav') is selected, then all tests pass

The only effect that set_video_backend('video_reader') has over test_io.py is related to the codecs used to encode/decode the test videos:

That means that under the current circumstances test_io is only testing the video_reader backend, rather than the PyAV one.

@andfoy this is great debugging, thanks!

So, test_io_opt is there to test the video_reader backend of read_video, without having to resort to copy-pasting all the tests. If it is negatively interfering with test_io, we should do something to change that.

It is great that we now know the reason why this wasn't working before, now we need to understand why the partial reading of files is not working with the video_reader backend.

@bjuncek you have used the video_reader backend for partial reads recently, right? Can you check again if those tests are passing or not in your system?

@fmassa I pulled your branch and run the tests in my PR. They are passing locally for me but that has always been the case so lets see what CI says

I think we can close this one