More tests for async* functions

tests/language/async_star_no_cancel_test.dart

+// Copyright (c) 2016, 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:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
+
+var events = [];
+
+ticker() async* {
+  var sc;
+  var sentTickCount = 0;
+  sc = new StreamController(onListen: () {
+    events.add("listen");
+  }, onCancel: () {
+    events.add("cancel");
+  });
+
+  try {
+    var counter = 0;
+    await for (var tick in sc.stream) {
+      counter++;

[Lasse Reichstein Nielsen, 2016/02/08 21:04:35]

Should there be a yield here?

Otherwise you have an async* function with no yield/yield* which means it is
unaffected by cancel.

[floitsch, 2016/02/09 16:56:34]

Yes. The tests now make sure that there is no cancel, if there isn't any
`yield`.

+    }
+  } finally {
+    events.add("finally");
+  }
+}
+
+void main() {
+  asyncStart();
+  events.add("main");
+  final subscription = ticker().listen((val) { });
+
+  bool cancelFinished = false;
+  // Cancel the subscription.
+  // The async* function is blocked on an `await` (the inner stream) and won't
+  // be able to complete.
+  Timer.run(() {
+    subscription.cancel().then((_) => cancelFinished = true);
+  });
+
+  new Timer(const Duration(milliseconds: 100), () {
+    Expect.isFalse(cancelFinished);
+    Expect.listEquals(["main", "listen"], events);
+    asyncEnd();
+  });
+}