Remove warnings in tests, and even fix analyzer hints.

test/subscription_stream_test.dart

Index: test/subscription_stream_test.dart
diff --git a/test/subscription_stream_test.dart b/test/subscription_stream_test.dart
index da77593e5918071088041b2c106d97dbbde4e1f2..03f0dddec203723465beb5679edbed44f787adc9 100644
--- a/test/subscription_stream_test.dart
+++ b/test/subscription_stream_test.dart
@@ -83,10 +83,10 @@ main() {
         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),