Add more tests for owners.py, remove unneeded code, make syntax errors more helpful

owners.py

 # Copyright (c) 2010 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 re
 
 
 # If this is present by itself on a line, this means that everyone can review.
 EVERYONE = '*'
 
 
 # Recognizes 'X@Y' email addresses. Very simplistic.
 BASIC_EMAIL_REGEXP = r'^[\w\-\+\%\.]+\@[\w\-\+\%\.]+$'
 
 
 class SyntaxErrorInOwnersFile(Exception):
-  def __init__(self, path, line, msg):
-    super(SyntaxErrorInOwnersFile, self).__init__((path, line, msg))
+  def __init__(self, path, lineno, msg):
+    super(SyntaxErrorInOwnersFile, self).__init__((path, lineno, msg))
     self.path = path
-    self.line = line
+    self.lineno = lineno
     self.msg = msg
 
   def __str__(self):
-    if self.msg:
-      return "%s:%d syntax error: %s" % (self.path, self.line, self.msg)
-    else:
-      return "%s:%d syntax error" % (self.path, self.line)
+    return "%s:%d syntax error: %s" % (self.path, self.lineno, self.msg)
 
 
 class Database(object):
   """A database of OWNERS files for a repository.
 
   This class allows you to find a suggested set of reviewers for a list
   of changed files, and see if a list of changed files is covered by a
   list of reviewers."""
 
   def __init__(self, root, fopen, os_path):
@@ skipping 94 matching lines @@
 
     lineno = 0
     for line in self.fopen(owners_path):
       lineno += 1
       line = line.strip()
       if line.startswith('#'):
         continue
       if line == 'set noparent':
         self.stop_looking.add(dirpath)
         continue
+      if line.startswith('set '):
+        raise SyntaxErrorInOwnersFile(owners_path, lineno,
+            'unknown option: "%s"' % line[4:].strip())
       if self.email_regexp.match(line) or line == EVERYONE:
         self.owned_by.setdefault(line, set()).add(dirpath)
         self.owners_for.setdefault(dirpath, set()).add(line)
         continue
-      raise SyntaxErrorInOwnersFile(owners_path, lineno, line)
+      raise SyntaxErrorInOwnersFile(owners_path, lineno,
+            ('line is not a comment, a "set" directive, '
+             'or an email address: "%s"' % line))
 
   def _covering_set_of_owners_for(self, files):
     # TODO(dpranke): implement the greedy algorithm for covering sets, and
     # consider returning multiple options in case there are several equally
     # short combinations of owners.
     every_owner = set()
     for f in files:
       dirname = self.os_path.dirname(f)
       while dirname in self.owners_for:
         every_owner |= self.owners_for[dirname]
         if self._stop_looking(dirname):
           break
         dirname = self.os_path.dirname(dirname)
     return every_owner