Make randomizing of listdir results optional

- the default is to not randomize
- can be changed by setting fs.shuffle_listdir_results to True
- see #647

Author: mrbean-bremen

CHANGES.md

@@ -3,6 +3,13 @@ The released versions correspond to PyPi releases.
 
 ## Version 4.6.0 (as yet unreleased)
 
+### Changes
+* `os.listdir`, `os.scandir` and `pathlib.Path.listdir` now return the
+  directory list in a random order only if explicitly configured in the 
+  file system (use `fs.shuffle_listdir_results = True` with `fs` being the 
+  file system). In a future version, the default may be changed to better 
+  reflect the real filesystem behavior (see [#647](../../issues/647))
+  
 ## [Version 4.5.2](https://pypi.python.org/pypi/pyfakefs/4.5.2) (2021-11-07)
 This is a bugfix release.
 

pyfakefs/fake_filesystem.py

@@ -957,6 +957,7 @@ def __init__(self, path_separator: str = os.path.sep,
         self.dev_null = FakeNullFile(self)
         # set from outside if needed
         self.patch_open_code = PatchMode.OFF
+        self.shuffle_listdir_results = False
 
     @property
     def is_linux(self) -> bool:
@@ -3227,16 +3228,17 @@ def listdir(self, target_directory: AnyStr) -> List[AnyStr]:
 
         Returns:
             A list of file names within the target directory in arbitrary
-            order. Note that the order is intentionally not the same in
-            subsequent calls to avoid tests relying on any ordering.
+            order. If `shuffle_listdir_results` is set, the order is not the
+            same in subsequent calls to avoid tests relying on any ordering.
 
         Raises:
             OSError: if the target is not a directory.
         """
         target_directory = self.resolve_path(target_directory, allow_fd=True)
         directory = self.confirmdir(target_directory)
         directory_contents = list(directory.entries.keys())
-        random.shuffle(directory_contents)
+        if self.shuffle_listdir_results:
+            random.shuffle(directory_contents)
         return directory_contents  # type: ignore[return-value]
 
     def __str__(self) -> str: