Revert Windows-specific optimization for mounting c drive

- can break tests under some conditions
- see #573

CHANGES.md

@@ -4,6 +4,8 @@ The released versions correspond to PyPi releases.
 ## Version 4.4.0 (as yet unreleased)
 
 ### Fixes
+* Reverted one Windows-specific optimization that can break tests under some
+  conditions (see [#573](../../issues/573))
 * Setting `os` did not reset `os.sep` and related variables,
   fixed null device name, added `os.pathsep` and missing `os.path` variables
   (see [#572](../../issues/572))

pyfakefs/fake_filesystem.py

@@ -1020,17 +1020,6 @@ def _starts_with_sep(self, path):
         return (path.startswith(sep) or altsep is not None and
                 path.startswith(altsep))
 
-    def _add_c_drive(self):
-        """Optimized version for the default Windows C drive.
-        For internal use only.
-        """
-        if self.is_windows_fs:
-            self.last_dev += 1
-            self.mount_points['C:'] = {
-                'idev': self.last_dev, 'total_size': None, 'used_size': 0
-            }
-            self.root.get_entry('C:') .st_dev = self.last_dev
-
     def add_mount_point(self, path, total_size=None):
         """Add a new mount point for a filesystem device.
         The mount point gets a new unique device number.
@@ -2323,15 +2312,14 @@ def make_string_path(self, path):
         fake_sep = matching_string(path, self.path_separator)
         return path.replace(os_sep, fake_sep)
 
-    def create_dir(self, directory_path, perm_bits=PERM_DEF, check=True):
+    def create_dir(self, directory_path, perm_bits=PERM_DEF):
         """Create `directory_path`, and all the parent directories.
 
         Helper method to set up your test faster.
 
         Args:
             directory_path: The full directory path to create.
             perm_bits: The permission bits as set by `chmod`.
-            check: For internal use only.
 
         Returns:
             The newly created FakeDirectory object.
@@ -2340,11 +2328,10 @@ def create_dir(self, directory_path, perm_bits=PERM_DEF, check=True):
             OSError: if the directory already exists.
         """
         directory_path = self.make_string_path(directory_path)
-        if check:
-            directory_path = self.absnormpath(directory_path)
-            self._auto_mount_drive_if_needed(directory_path)
-            if self.exists(directory_path, check_link=True):
-                self.raise_os_error(errno.EEXIST, directory_path)
+        directory_path = self.absnormpath(directory_path)
+        self._auto_mount_drive_if_needed(directory_path)
+        if self.exists(directory_path, check_link=True):
+            self.raise_os_error(errno.EEXIST, directory_path)
         path_components = self._path_components(directory_path)
         current_dir = self.root
 
@@ -2357,10 +2344,10 @@ def create_dir(self, directory_path, perm_bits=PERM_DEF, check=True):
                 current_dir.add_entry(new_dir)
                 current_dir = new_dir
             else:
-                if check and S_ISLNK(directory.st_mode):
+                if S_ISLNK(directory.st_mode):
                     directory = self.resolve(directory.contents)
                 current_dir = directory
-                if check and directory.st_mode & S_IFDIR != S_IFDIR:
+                if directory.st_mode & S_IFDIR != S_IFDIR:
                     self.raise_os_error(errno.ENOTDIR, current_dir.path)
 
         # set the permission after creating the directories

pyfakefs/fake_filesystem_unittest.py

@@ -734,8 +734,7 @@ def setUp(self, doctester=None):
 
         # the temp directory is assumed to exist at least in `tempfile1`,
         # so we create it here for convenience
-        self.fs.create_dir(temp_dir, check=False)
-        self.fs._add_c_drive()
+        self.fs.create_dir(temp_dir)
 
     def start_patching(self):
         if not self._patching: