AttributeError: 'FakePipeWrapper' object has no attribute 'readable'

[MasterSergius]

Describe the bug
I have a set of tests using fake fs and vcr cassetess. When I try to run it, I have the following error:

            if c2pread != -1:
                self.stdout = io.open(c2pread, 'rb', bufsize)
                if self.text_mode:
>                   self.stdout = io.TextIOWrapper(self.stdout,
                            encoding=encoding, errors=errors)
E                           AttributeError: 'FakePipeWrapper' object has no attribute 'readable'
subprocess.py:850: AttributeError

This error appeared when I tried to run tests in a bit newer environment:

Python              3.8.12
-----------------------
pyfakefs           4.5.3
pytest              6.2.5
pytest-asyncio     0.16.0
pytest-mock        3.6.1
pytest-recording   0.12.0

It works within the following (older) environment:

Python              3.8.2
-----------------------
pyfakefs                          4.3.0
pytest                            6.1.2
pytest-asyncio                    0.14.0
pytest-mock                       3.3.1
pytest-recording                  0.10.0

How To Reproduce
pytest --record-mode=once tests

[mrbean-bremen]

Hm, can you show your actual test, or a minimal reproducible example? Are you using subprocess or multiprocessing in your tested code? Both are known to have problems with pyfakefs. Though given that it is the pytest environment that has changed, it probably is an incompatibility with one of the other plugins...

[MasterSergius]

Ok, I wanted to contribute to this library https://github.com/okta/okta-sdk-python, so I tried to run tests if everything is fine, you can check tests/integration folder

[mrbean-bremen]

Ok, I will check if I can reproduce it, thanks.

[mrbean-bremen]

What OS you are using? I'm currently under Windows, and here this is not reproducible with the same environment.

[MasterSergius]

MacOS 10.15.17

[mrbean-bremen]

Ok, I just checked their own CI tests which use the same versions under Ubuntu and also work, so I guess this is a MacOS-specific problem. Unfortunately, I don't have a Mac, so I'm not sure how to reproduce this, but I'm afraid it has to with subprocess using some OS-specific functions. As mentioned, subprocess does not always work with pyfakefs due to that (pyfakefs cannot only patch Python functions, not C functions), and I just noticed that the callstack is indeed in subprocess.py. I will have a look at that code, but I'm afraid that you are out of luck here.
If you want to contribute to that repo, you probably have to rely on their CI for the time being.

[mrbean-bremen]

I checked the code, and I may actually be able to fix this - maybe all it takes is to patch a couple of functions for the fake pipe. I cannot guarantee that it will work after the fix, but we can try it.

[MasterSergius]

@mrbean-bremen ok, anyway, thank you for the fast response

[mrbean-bremen]

@MasterSergius - can you please check how it behaves with pyfakefs master?

[MasterSergius]

@mrbean-bremen Looks fine, it works

[mrbean-bremen]

Ok, thanks - do you need a patch release?

[MasterSergius]

No, I can use it now, so you can release when u're ready to.

[mrbean-bremen]

Ok, thanks - closing this then.

[julienschuermans]

Hi @mrbean-bremen, thanks for your amazing work!
I've got the same issue. When are you planning to release the fix?

[mrbean-bremen]

I can make a patch release tonight, if you need it.

[julienschuermans]

That would be great, thanks a lot!

[mrbean-bremen]

Ok, done.