_add_c_drive() failure when user does not have access to c:

[stephenfuqua]

Describe the bug

When using pyfakefs 4.3.0 with pytest, the patcher's setUp function calls _add_c_drive. This works when I execute locally or on my build server when executed manually. It fails, however, when run by the build server using a service account. I think the problem is that the service account does not have access to read the C: drive. Side note: for these tests I actually want to simulate a Linux filesystem. The setUp function is setting up C: before I can intercept the fs object and set the os to Linux.

Final parts of the stack trace:

...\lib\site-packages\pyfakefs\fake_filesystem_unittest.py:727: in setUp
    self.fs._add_c_drive()
...\lib\site-packages\pyfakefs\fake_filesystem.py:1026: in _add_c_drive
    self.root.get_entry('C:') .st_dev = self.last_dev
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <pyfakefs.fake_filesystem.FakeDirectory object at 0x0000023C9DD61610>
pathname_name = 'C:'

    def get_entry(self, pathname_name):
        """Retrieves the specified child file or directory entry.
    
        Args:
            pathname_name: The basename of the child object to retrieve.
    
        Returns:
            The fake file or directory object.
    
        Raises:
            KeyError: if no child exists by the specified name.
        """
        pathname_name = self._normalized_entryname(pathname_name)
>       return self.contents[to_string(pathname_name)]
E       KeyError: 'C:'

How To Reproduce

1. Install pytest (6.1.2) and pyfakefs (4.3.0)

2. Create a simple test like the following:

   import pytest
   
   def describe_will_this_fail():
       @pytest.fixture
       def fixture(fs):
           fs.os = "linux"
   
       def it_should_not_fail(fs, fixture):
           assert 1 == 1
   

3. Run pytest from an account that does not have access to C:.

Your enviroment

Windows-10-10.0.17763-SP0
Python 3.8.6 (tags/v3.8.6:db45529, Sep 23 2020, 15:52:53) [MSC v.1927 64 bit (AMD64)]
pyfakefs 4.3.0

[stephenfuqua]

I will try to make time to debug further and see if I can offer a patch. For now I've reverted to an older version.

[mrbean-bremen]

Thanks - that was a kind of micro-optimization that probably was too fragile. I think I'll just revert that (Windows-specific) optimization, I didn't like it anyway. It will add a millisecond to the test setup under Windows, but I can check later if this can be optimized in a nicer way.

[mrbean-bremen]

Please check if the current master works for you, and if you need a patch release.

[stephenfuqua]

Yes, that works. Thank you.

Test process: I created a temporary build configuration in TeamCity so that I could closely replicate the original process. In this configuration wrote a small script that installs pytest and pyfakefs from the canonical sources and runs the sample above. As expected, execution failed. Then I modified the build configuration to clone this repository and install the local clone into the virtual environment. Build configuration now succeeds.

[mrbean-bremen]

Thanks! I didn't add a regression test, as this was basically a revert, but had to ensure that it works in your use case.
Do you need a patch release with the fix?

[stephenfuqua]

Patch release would be convenient, but it is not necessary. We can wait until the next one.

[mrbean-bremen]

Ok, thanks - in this case I will wait if something else comes up, and probably make a patch in a couple of weeks.
Closing this as fixed.

[mrbean-bremen]

The bugfix release is out now.