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

tests/owners_unittest.py

 #!/usr/bin/python
 # Copyright (c) 2011 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.
 
 """Unit tests for owners.py."""
 
 import unittest
 
 import owners
@@ skipping 54 matching lines @@
   def test_covered_by__everyone(self):
     self.assert_covered_by(['DEPS'], [john])
     self.assert_covered_by(['DEPS'], [darin])
 
   def test_covered_by__explicit(self):
     self.assert_covered_by(['content/content.gyp'], [john])
     self.assert_covered_by(['chrome/gpu/OWNERS'], [ken])
 
   def test_covered_by__owners_propagates_down(self):
     self.assert_covered_by(['chrome/gpu/OWNERS'], [ben])
+
+  def test_covered_by__no_file_in_dir(self):
     self.assert_covered_by(['/chrome/renderer/gpu/gpu_channel_host.h'], [peter])
 
   def assert_not_covered_by(self, files, reviewers, unreviewed_files):
     db = self.db()
     self.assertEquals(db.files_not_covered_by(set(files), set(reviewers)),
                       set(unreviewed_files))
 
   def test_not_covered_by__need_at_least_one_reviewer(self):
     self.assert_not_covered_by(['DEPS'], [], ['DEPS'])
 
@@ skipping 22 matching lines @@
   def test_reviewers_for__set_noparent_works(self):
     self.assert_reviewers_for(['content/content.gyp'], [john, darin])
 
   def test_reviewers_for__wildcard_dir(self):
     self.assert_reviewers_for(['DEPS'], [owners.EVERYONE])
 
   def assert_syntax_error(self, owners_file_contents):
     db = self.db()
     self.files['/foo/OWNERS'] = owners_file_contents
     self.files['/foo/DEPS'] = ''
-    self.assertRaises(owners.SyntaxErrorInOwnersFile, db.reviewers_for,
-      ['/foo/DEPS'])
+    try:
+      db.reviewers_for(['/foo/DEPS'])
+      self.fail()  # pragma: no cover
+    except owners.SyntaxErrorInOwnersFile, e:
+      self.assertTrue(str(e).startswith('/foo/OWNERS:1'))
 
   def test_syntax_error__unknown_token(self):
     self.assert_syntax_error('{}\n')
 
   def test_syntax_error__unknown_set(self):
     self.assert_syntax_error('set myfatherisbillgates\n')
 
   def test_syntax_error__bad_email(self):
     self.assert_syntax_error('ben\n')
 
 
 if __name__ == '__main__':
   unittest.main()