Fix ValueError: I/O operation on closed file during tests

[yunzheng]

Sometimes the stdout file object is closed by flow.record internals as it is sometimes mocked and swapped by pytest during tests which in turn can confuse is_stdout() to return False causing the file to be closed.

This is now fixed by adding two custom methods for getting the stdio streams:

• flow.record.utils.get_stdout()
• flow.record.utils.get_stdin()

These methods are the preferred way to get the stdio streams as they also set an extra attribute on the returned file object that is checked by is_stdout().

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.76%. Comparing base (0865b50) to head (ca4f7e1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #123      +/-   ##
==========================================
+ Coverage   83.72%   83.76%   +0.04%     
==========================================
  Files          34       34              
  Lines        3403     3413      +10     
==========================================
+ Hits         2849     2859      +10     
  Misses        554      554              

Flag	Coverage Δ
unittests	83.76% <100.00%> (+0.04%)	⬆️

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[yunzheng]

This sadly didn't fix the issue :(

Will leave this PR in Draft state for more adhoc tests.

[yunzheng]

Took a while but this should now be fixed. I took quite a deep dive into the pytest internals to figure out the cause.

It's mainly caused due to pytest's capture.py swapping sys.stdout with it's own objects (which is fine btw), however in our own code we check the file objects by comparing them to sys.stdout or sys.stdout.buffer, but as sys.stdout keeps getting swapped multiple times (eg: nested pytest operations/fixtures) it could be that a file object that was once a sys.stdout file is now not seen as stdout anymore, and therefore closed by flow.record internals at certain points.

The easiest fix was to ensure that when we request a stdout stream in flow.record to mark them as stdout ourselves, and ensure that they don't get closed.

I have no idea why this only happened on PyPy. Could be a race condition.