Change pathlib.Path.owner()/group() to behave like real os

- both methods now look up the real user/group name for the user/group id
  that is associated with the fake file
- assumes a valid user and group id is set
- closes pytest-dev#678

CHANGES.md

@@ -8,12 +8,16 @@ The released versions correspond to PyPi releases.
   longer officially supported by pyfakefs
   ** `os.stat_float_times` has been removed in Python 3.7 and is therefore no 
      longer supported
-* added some support for the upcoming Python version 3.11
-  (see [#677](../../issues/677))
 * under Windows, the root path is now effectively `C:\` instead of `\`; a 
   path starting with `\` points to the current drive as in the real file 
   system (see [#673](../../issues/673))
+* fake `pathlib.Path.owner()` and `pathlib.Path.group()` now behave like the 
+  real methods - they look up the real user/group name for the user/group id
+  that is associated with the fake file (see [#678](../../issues/678))
 
+### New Features
+* added some support for the upcoming Python version 3.11
+  (see [#677](../../issues/677))
 
 ## [Version 4.5.6](https://pypi.python.org/pypi/pyfakefs/4.5.6) (2022-03-17)
 Fixes a regression which broke tests with older pytest versions (< 3.9).

pyfakefs/fake_pathlib.py

@@ -754,20 +754,22 @@ class PosixPath(FakePath, PurePosixPath):
         __slots__ = ()
 
         def owner(self):
-            """Return the current user name. It is assumed that the fake
-            file system was created by the current user.
+            """Return the username of the file owner.
+             It is assumed that `st_uid` is related to a real user,
+             otherwise `KeyError` is raised.
             """
             import pwd
 
-            return pwd.getpwuid(os.getuid()).pw_name
+            return pwd.getpwuid(self.stat().st_uid).pw_name
 
         def group(self):
-            """Return the current group name. It is assumed that the fake
-            file system was created by the current user.
+            """Return the group name of the file group.
+            It is assumed that `st_gid` is related to a real group,
+            otherwise `KeyError` is raised.
             """
             import grp
 
-            return grp.getgrgid(os.getgid()).gr_name
+            return grp.getgrgid(self.stat().st_gid).gr_name
 
     Path = FakePath
 

pyfakefs/tests/fake_pathlib_test.py

@@ -26,6 +26,8 @@
 import stat
 import sys
 import unittest
+from collections import namedtuple
+from unittest import mock
 
 from pyfakefs import fake_pathlib, fake_filesystem, fake_filesystem_unittest
 from pyfakefs.fake_filesystem import is_root
@@ -1073,12 +1075,37 @@ def test_truncate(self):
     @unittest.skipIf(sys.platform == 'win32',
                      'no pwd and grp modules in Windows')
     def test_owner_and_group_posix(self):
-        self.check_posix_only()
         path = self.make_path('some_file')
         self.create_file(path)
         self.assertTrue(self.path(path).owner())
         self.assertTrue(self.path(path).group())
 
+    @unittest.skipIf(sys.platform == 'win32',
+                     'no pwd and grp modules in Windows')
+    def test_changed_owner_and_group(self):
+        def fake_getpwuid(uid):
+            if uid == 42:
+                user_struct = namedtuple('user', 'pw_name, pw_uid')
+                user_struct.pw_name = 'NewUser'
+                return user_struct
+            raise KeyError
+
+        def fake_getgrgid(uid):
+            if uid == 5:
+                group_struct = namedtuple('group', 'gr_name, gr_gid')
+                group_struct.gr_name = 'NewGroup'
+                return group_struct
+            raise KeyError
+
+        self.skip_real_fs()
+        path = self.make_path('some_file')
+        self.create_file(path)
+        self.os.chown(path, 42, 5)
+        with mock.patch('pwd.getpwuid', fake_getpwuid):
+            with mock.patch('grp.getgrgid', fake_getgrgid):
+                self.assertEqual('NewUser', self.path(path).owner())
+                self.assertEqual('NewGroup', self.path(path).group())
+
     def test_owner_and_group_windows(self):
         self.check_windows_only()
         path = self.make_path('some_file')