Working with shared objects .so

[danicc097]

Describe the bug
I ran into some testing issues with Ghostscript, which requires some shared objects to be available.

How To Reproduce
Install ghostscript via your system package manager and the python library ghostscript.

class TestGhostscript:
    def test_installed(self, fs):
        from ctypes.util import find_library

        print(find_library("gs")) # expected 'libgs.so.9'

        assert find_library("gs") is not None

this will fail. Remove fs and test passes.

Is there a workaround for this?

NOTE this fails both locally and running in docker with python:3.9.5-slim-buster

Your environment

Linux-5.4.0-137-generic-x86_64-with-glibc2.31
Python 3.9.5 (default, Aug  3 2022, 11:09:29) 
[GCC 9.4.0]
pytest 7.1.0
pyfakefs 4.5.6

[mrbean-bremen]

Strange.. thanks for the report, I will see what I can find out.

[mrbean-bremen]

Sorry it so long to get to this, but I'm afraid you run into a limitation of pyfakefs here. find_library internally calls subprocess.Popen on /sbin/ldconfig, and subprocess is known to not work well with pyfakefs. It won't even work if you map the real executable into the fake filesystem.

So short of mocking out find_library to return the desired value there is nothing you can do here.

I'm going to convert this into a discussion Q/A issue so it remains visible. I may also add a line about find_library in the documentation.