Readd missing unittests for owners

owners.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """A database of OWNERS files."""
 
 import collections
 import re
 
 
@@ skipping 160 matching lines @@
       dirs.add(self.os_path.dirname(f))
 
     owned_dirs = {}
     dir_owners = {}
 
     for current_dir in dirs:
       # Get the list of owners for each directory.
       current_owners = set()
       dirname = current_dir
       while dirname in self.owners_for:
-        for owner in self.owners_for[dirname]:
-          current_owners.add(owner)
+        current_owners |= self.owners_for[dirname]
         if self._stop_looking(dirname):
           break
+        prev_parent = dirname
         dirname = self.os_path.dirname(dirname)
+        if prev_parent == dirname:
+          break
 
       # Map each directory to a list of its owners.
       dir_owners[current_dir] = current_owners
 
       # Add the directory to the list of each owner.
       for owner in current_owners:
-        if not owner in owned_dirs:
-          owned_dirs[owner] = set()
-        owned_dirs[owner].add(current_dir)
+        owned_dirs.setdefault(owner, set()).add(current_dir)
 
     final_owners = set()
     while dirs:
       # Find the owner that has the most directories.
       max_count = 0
       max_owner = None
       owner_count = {}
       for dirname in dirs:
         for owner in dir_owners[dirname]:
           count = owner_count.get(owner, 0) + 1
           owner_count[owner] = count
           if count >= max_count:
             max_owner = owner
+            max_count = count
 
       # If no more directories have OWNERS, we're done.
       if not max_owner:
         break
 
       final_owners.add(max_owner)
 
       # Remove all directories owned by the current owner from the remaining
       # list.
       for dirname in owned_dirs[max_owner]:
-        if dirname in dirs:
-          dirs.remove(dirname)
+        dirs.discard(dirname)
 
     return final_owners