No PermissionError gets raised on deleting a read-only file

[g3n35i5]

Describe the bug
I'm trying to modify a file in a unittest so that it is in read-only mode and therefore non-deletable unless the user has root privileges.

How To Reproduce
Run the following unittest class:

#!/usr/bin/env python3

import os
import stat

from pyfakefs.fake_filesystem_unittest import TestCase


class TestCaseExample(TestCase):
    def setUp(self):
        self.setUpPyfakefs()

    def test_delete_file_insufficient_permissions(self):
        file_path = "/tmp/file.txt"
        file_content = "Doesn't really matter but hey :)"

        self.fs.create_file(file_path, contents=file_content)
        self.assertTrue(os.path.exists(file_path))

        # Make sure we're not admin
        self.assertFalse(os.getuid() == 0)

        # Make sure that the default mask is -rw-rw-rw
        default_mask = 0o666
        initial_mask = stat.S_IMODE(os.lstat(file_path).st_mode)
        self.assertEqual(default_mask, initial_mask)

        # Make sure that the new mask is -r--r--r--
        read_only_mask = 0o444
        os.chmod(file_path, read_only_mask)
        new_mask = stat.S_IMODE(os.lstat(file_path).st_mode)
        self.assertEqual(read_only_mask, new_mask)

        # Deleting the file should not be possible
        with self.assertRaises(PermissionError):
            os.remove(file_path)

Expected result: The test runs without errors, because the file is in read-only mode and the user is not privileged and therefore must not delete the file.

Actual result: The test fails

Ran 1 test in 0.051s

FAILED (failures=1)

Failure
Traceback (most recent call last):
  File "/usr/lib/python3.8/unittest/case.py", line 60, in testPartExecutor
    yield
  File "/usr/lib/python3.8/unittest/case.py", line 676, in run
    self._callTestMethod(testMethod)
  File "/usr/lib/python3.8/unittest/case.py", line 633, in _callTestMethod
    method()
  File "/tmp/pyfakefs-permissions/main.py", line 36, in test_delete_file_insufficient_permissions
    os.remove(file_path)
  File "/usr/lib/python3.8/unittest/case.py", line 227, in __exit__
    self._raiseFailure("{} not raised".format(exc_name))
  File "/usr/lib/python3.8/unittest/case.py", line 164, in _raiseFailure
    raise self.test_case.failureException(msg)
AssertionError: PermissionError not raised

Your enviroment
Linux-5.7.12-arch1-1-x86_64-with-glibc2.2.5
Python 3.8.5 (default, Jul 27 2020, 08:42:51)
[GCC 10.1.0]
pyfakefs 4.1.0

Notes
Even if I explicitly initialize the environment as non-privileged self.setUpPyfakefs(allow_root_user=False) the problem still exists

Possibly related issues

• pyfakefs seemingly ignores file permissions on write() #489
• ability to run code as non-root #474

[mrbean-bremen]

This is intentionally. Under Unix (not Windows), you can remove such a file, as long as the file directory has write permissions. Here ist the respective test in pyfakefs (in fake_os_test.py):

    def test_remove_file_with_read_permission_shall_succeed_in_posix(self):
        self.check_posix_only()
        path = self.make_path('foo', 'bar')
        self.create_file(path)
        self.os.chmod(path, 0o444)
        self.os.remove(path)
        self.assertFalse(self.os.path.exists(path))

Note that this test (like most pyfakefs tests) runs both in pyfakefs and in the real fs to ensure that the behavior is the same.

[g3n35i5]

Thank you for the clarification, I hadn't considered that...