Add a dedicated Result for skipped tests.

test/runner/engine_test.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.
 
 import 'dart:async';
 
 import 'package:test/src/backend/group.dart';
 import 'package:test/src/backend/state.dart';
 import 'package:test/src/runner/engine.dart';
 import 'package:test/src/runner/plugin/environment.dart';
@@ skipping 154 matching lines @@
       });
 
       var engine = new Engine.withSuites([
         new RunnerSuite(const PluginEnvironment(), new Group.root(tests))
       ]);
 
       engine.onTestStarted.listen(expectAsync((liveTest) {
         expect(liveTest, same(engine.liveTests.single));
         expect(liveTest.test.name, equals(tests.single.name));
 
-        var first = true;
+        var i = 0;
         liveTest.onStateChange.listen(expectAsync((state) {
-          expect(state, equals(first
-              ? const State(Status.running, Result.success)
-              : const State(Status.complete, Result.success)));
-          first = false;
-        }, count: 2));
+          if (i == 0) {
+            expect(state, equals(const State(Status.running, Result.success)));
+          } else if (i == 1) {
+            expect(state, equals(const State(Status.running, Result.skipped)));
+          } else if (i == 2) {
+            expect(state, equals(const State(Status.complete, Result.skipped)));
+          }
+          i++;
+        }, count: 3));
 
         expect(liveTest.onComplete, completes);
       }));
 
       return engine.run();
     });
   });
 }