Refactor groups to pipe them through to the runner.

lib/src/runner.dart

 // Copyright (c) 2015, 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.
 
 library test.runner;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:async/async.dart';
@@ skipping 141 matching lines @@
       if (new Directory(path).existsSync()) return _loader.loadDir(path);
       if (new File(path).existsSync()) return _loader.loadFile(path);
 
       return new Stream.fromIterable([
         new LoadSuite("loading $path", () =>
             throw new LoadException(path, 'Does not exist.'))
       ]);
     })).map((loadSuite) {
       return loadSuite.changeSuite((suite) {
         if (_config.pattern == null) return suite;
-        return suite.change(tests: suite.tests.where((test) =>
-            test.name.contains(_config.pattern)));
+        return suite.filter((test) => test.name.contains(_config.pattern));
       });
     });
   }
 
   /// Loads each suite in [suites] in order, pausing after load for platforms
   /// that support debugging.
   Future<bool> _loadThenPause(Stream<LoadSuite> suites) async {
     if (_config.platforms.contains(TestPlatform.vm)) {
       warn("Debugging is currently unsupported on the Dart VM.",
           color: _config.color);
@@ skipping 73 matching lines @@
 
       await inCompletionOrder([
         suite.environment.displayPause(),
         cancelableNext(stdinLines)
       ]).first;
     } finally {
       _reporter.resume();
     }
   }
 }