Add support for setUpAll and tearDownAll.

lib/src/backend/group.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.backend.group;
 
 import 'metadata.dart';
 import 'operating_system.dart';
 import 'group_entry.dart';
 import 'test.dart';
 import 'test_platform.dart';
 
 /// A group contains one or more tests and subgroups.
 ///
 /// It includes metadata that applies to all contained tests.
 class Group implements GroupEntry {
   final String name;
 
   final Metadata metadata;
 
   /// The children of this group.
   final List<GroupEntry> entries;
 
   /// Returns a new root-level group.
   Group.root(Iterable<GroupEntry> entries, {Metadata metadata})
       : this(null, entries, metadata: metadata);
 
-  Group(this.name, Iterable<GroupEntry> entries, {Metadata metadata})
+  /// A test to run before all tests in the group.
+  ///
+  /// This is `null` if no `setUpAll` callbacks were declared.
+  final Test setUpAll;
+
+  /// A test to run after all tests in the group.
+  ///
+  /// This is `null` if no `tearDown` callbacks were declared.
+  final Test tearDownAll;
+
+  Group(this.name, Iterable<GroupEntry> entries, {Metadata metadata,
+          Test this.setUpAll, Test this.tearDownAll})
       : entries = new List<GroupEntry>.unmodifiable(entries),
         metadata = metadata == null ? new Metadata() : metadata;
 
   Group forPlatform(TestPlatform platform, {OperatingSystem os}) {
     if (!metadata.testOn.evaluate(platform, os: os)) return null;
     var newMetadata = metadata.forPlatform(platform, os: os);
     var filtered = _map((entry) => entry.forPlatform(platform, os: os));
     if (filtered.isEmpty) return null;
-    return new Group(name, filtered, metadata: newMetadata);
+    return new Group(name, filtered,
+        metadata: newMetadata, setUpAll: setUpAll, tearDownAll: tearDownAll);
   }
 
   Group filter(bool callback(Test test)) {
     var filtered = _map((entry) => entry.filter(callback));
     if (filtered.isEmpty) return null;
-    return new Group(name, filtered, metadata: metadata);
+    return new Group(name, filtered,
+        metadata: metadata, setUpAll: setUpAll, tearDownAll: tearDownAll);
   }
 
   /// Returns the entries of this group mapped using [callback].
   ///
   /// Any `null` values returned by [callback] will be removed.
   List<GroupEntry> _map(GroupEntry callback(GroupEntry entry)) {
     return entries
         .map((entry) => callback(entry))
         .where((entry) => entry != null)
         .toList();
   }
 }