Add a testOn parameter to test() and group().

lib/src/backend/declarer.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 unittest.backend.declarer;
 
 import 'dart:collection';
 
 import 'group.dart';
 import 'invoker.dart';
+import 'metadata.dart';
 import 'test.dart';
 
 /// A class that manages the state of tests as they're declared.
 ///
 /// This is in charge of tracking the current group, set-up, and tear-down
 /// functions. It produces a list of runnable [tests].
 class Declarer {
   /// The current group.
   var _group = new Group.root();
 
   /// The list of tests that have been defined.
   List<Test> get tests => new UnmodifiableListView<Test>(_tests);
   final _tests = new List<Test>();
 
   Declarer();
 
   /// Defines a test case with the given description and body.
   ///
   /// The description will be added to the descriptions of any surrounding
   /// [group]s.
-  void test(String description, body()) {
+  ///
+  /// If [testOn] is passed, it's parsed as a [PlatformSelector], and the test
+  /// will only be run on matching platforms.
+  void test(String description, body(), {String testOn}) {
     // TODO(nweiz): Once tests have begun running, throw an error if [test] is
     // called.
     var prefix = _group.description;
     if (prefix != null) description = "$prefix $description";
 
+    var metadata = _group.metadata.merge(new Metadata.parse(testOn: testOn));
     var group = _group;
-    _tests.add(new LocalTest(description, () {
+    _tests.add(new LocalTest(description, metadata, () {
       // TODO(nweiz): It might be useful to throw an error here if a test starts
       // running while other tests from the same declarer are also running,
       // since they might share closurized state.
       return group.runSetUp().then((_) => body());
     }, tearDown: group.runTearDown));
   }
 
   /// Creates a group of tests.
   ///
   /// A group's description is included in the descriptions of any tests or
   /// sub-groups it contains. [setUp] and [tearDown] are also scoped to the
   /// containing group.
-  void group(String description, void body()) {
+  ///
+  /// If [testOn] is passed, it's parsed as a [PlatformSelector], and any tests
+  /// in the group will only be run on matching platforms.
+  void group(String description, void body(), {String testOn}) {
     var oldGroup = _group;
-    _group = new Group(oldGroup, description);
+
+    _group = new Group(
+        oldGroup, description, new Metadata.parse(testOn: testOn));
     try {
       body();
     } finally {
       _group = oldGroup;
     }
   }
 
   /// Registers a function to be run before tests.
   ///
   /// This function will be called before each test is run. [callback] may be
@@ skipping 21 matching lines @@
   /// groups or at the top level.
   void tearDown(callback()) {
     if (_group.tearDown != null) {
       throw new StateError("tearDown() may not be called multiple times for "
           "the same group.");
     }
 
     _group.tearDown = callback;
   }
 }