Don't test for file differences in the polling watcher.

pkg/watcher/test/directory_watcher/mac_os_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:scheduled_test/scheduled_test.dart';
 import 'package:watcher/src/directory_watcher/mac_os.dart';
 import 'package:watcher/watcher.dart';
 
 import 'shared.dart';
 import '../utils.dart';
@@ skipping 18 matching lines @@
     createDir("dir");
     writeFile("dir/old.txt");
     deleteDir("dir");
     createDir("dir");
 
     startWatcher(dir: "dir");
     writeFile("dir/newer.txt");
     expectAddEvent("dir/newer.txt");
   });
 
-  test('notifies even if the file contents are unchanged', () {
-    writeFile("a.txt", contents: "same");
-    writeFile("b.txt", contents: "before");
-    startWatcher();
-    writeFile("a.txt", contents: "same");
-    writeFile("b.txt", contents: "after");
-    expectModifyEvent("a.txt");
-    expectModifyEvent("b.txt");
-  });
-
   test('emits events for many nested files moved out then immediately back in',
       () {
     withPermutations((i, j, k) =>
         writeFile("dir/sub/sub-$i/sub-$j/file-$k.txt"));
 
     startWatcher(dir: "dir");
 
     renameDir("dir/sub", "sub");
     renameDir("sub", "dir/sub");
 
     inAnyOrder(() {
       withPermutations((i, j, k) =>
           expectRemoveEvent("dir/sub/sub-$i/sub-$j/file-$k.txt"));
     });
 
     inAnyOrder(() {
       withPermutations((i, j, k) =>
           expectAddEvent("dir/sub/sub-$i/sub-$j/file-$k.txt"));
     });
   });
 }