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[Python-Dev] Tests failing on Windows with TESTFN


25.07.18 18:07, Tim Golden ????:
> I'm just easing back into core development work by trying to get a 
> stable testing environment for Python development on Windows.
> 
> One problem is that certain tests use support.TESTFN (a local directory 
> constructed from the pid) for output files etc. However this can cause 
> issues on Windows when recreating the folders / files for multiple 
> tests, especially when running in parallel.
> 
> Here's an example on my laptop deliberately running 3 tests with -j0 
> which I know will generate an error about one time in three:
> 
> C:\work-in-progress\cpython>python -mtest -j0 test_urllib2 test_bz2 
> test_importlib
> 
> Running Debug|Win32 interpreter...
> Run tests in parallel using 6 child processes
> 0:00:23 [1/3/1] test_urllib2 failed
> test test_urllib2 failed -- Traceback (most recent call last):
>  ? File "C:\work-in-progress\cpython\lib\test\test_urllib2.py", line 
> 821, in test_file
>  ??? f = open(TESTFN, "wb")
> PermissionError: [Errno 13] Permission denied: '@test_15564_tmp'
> 
> Although these errors are both intermittent and fairly easily spotted, 
> the effect is that I rarely get a clean test run when I'm applying a patch.

Try to use test.support.unlink() instead of os.unlink(). It is purposed 
for solving this issue.

> I started to address this years ago but things stalled. I'm happy to 
> pick this up again and have another go, but I wanted to ask first 
> whether there was any objection to my converting tests to using tempfile 
> functions which should avoid the problem?

I think the only concern is that it is a pretty large change across many 
files, and there is a risk of introducing bugs. Also, creating a 
temporary file in setUp() may slowdown testing, especially if TESTFN is 
not needed in every test.