Remove warnings in tests, and even fix analyzer hints.

test/subscription_stream_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:async/async.dart" show SubscriptionStream;
 import "package:test/test.dart";
 
 import "utils.dart";
@@ skipping 65 matching lines @@
         setUp(() {
           var source = createErrorStream();
           var sourceSubscription = source.listen(null,
                                                  cancelOnError: sourceCancels);
           subscriptionStream = new SubscriptionStream<int>(sourceSubscription);
         });
 
         test("- subscriptionStream: no", () async {
           var done = new Completer();
           var events = [];
-          var subscription = subscriptionStream.listen(events.add,
-                                                       onError: events.add,
-                                                       onDone: done.complete,
-                                                       cancelOnError: false);
+          subscriptionStream.listen(events.add,
+                                    onError: events.add,
+                                    onDone: done.complete,
+                                    cancelOnError: false);
           var expected = [1, 2, "To err is divine!"];
           if (sourceCancels) {
             var timeout = done.future.timeout(const Duration(milliseconds: 5),
                                               onTimeout: () => true);
             expect(await timeout, true);
           } else {
             expected.add(4);
             await done.future;
           }
           expect(events, expected);
@@ skipping 67 matching lines @@
     controller.add(4);
     await flushMicrotasks();
     controller.close();
   }();
   return controller.stream;
 }
 
 Stream<int> createLongStream() async* {
   for (int i = 0; i < 200; i++) yield i;
 }