Add unit tests for watchlists

watchlists.py

 #!/usr/bin/python
 # Copyright (c) 2009 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.
 
 """Watchlists
 
 Watchlists is a mechanism that allow a developer (a "watcher") to watch over
 portions of code that he is interested in. A "watcher" will be cc-ed to
 changes that modify that portion of code, thereby giving him an opportunity
@@ skipping 27 matching lines @@
   _RULES_FILENAME = _RULES
   _repo_root = None
   _defns = {}       # Definitions
   _watchlists = {}  # name to email mapping
 
   def __init__(self, repo_root):
     self._repo_root = repo_root
     self._LoadWatchlistRules()
 
   def _GetRulesFilePath(self):
+    """Returns path to WATCHLISTS file."""
     return os.path.join(self._repo_root, self._RULES_FILENAME)
 
   def _HasWatchlistsFile(self):
     """Determine if watchlists are available for this repo."""
     return os.path.exists(self._GetRulesFilePath())
 
+  def _ContentsOfWatchlistsFile(self):
+    """Read the WATCHLISTS file and return its contents."""
+    try:
+      watchlists_file = open(self._GetRulesFilePath())
+      contents = watchlists_file.read()
+      watchlists_file.close()
+      return contents
+    except IOError, e:
+      logging.error("Cannot read %s: %s" % (self._GetRulesFilePath(), e))
+      return ''
+
   def _LoadWatchlistRules(self):
+    """Load watchlists from WATCHLISTS file. Does nothing if not present."""
     if not self._HasWatchlistsFile():
       return
-    watchlists_file = open(self._GetRulesFilePath())
-    contents = watchlists_file.read()
-    watchlists_file.close()
 
+    contents = self._ContentsOfWatchlistsFile()
     watchlists_data = None
     try:
       watchlists_data = eval(contents, {'__builtins__': None}, None)
     except SyntaxError, e:
       logging.error("Cannot parse %s. %s" % (self._GetRulesFilePath(), e))
       return
 
     defns = watchlists_data.get("WATCHLIST_DEFINITIONS")
     if not defns:
       logging.error("WATCHLIST_DEFINITIONS not defined in %s" %
@@ skipping 37 matching lines @@
     print "Usage (from the base of repo):"
     print "  %s [file-1] [file-2] ...." % argv[0]
     return 1
   wl = Watchlists(os.getcwd())
   watchers = wl.GetWatchersForPaths(argv[1:])
   print watchers
 
 
 if __name__ == '__main__':
   main(sys.argv)