Factor failing tests out of language/async_star_test.dart

tests/language/async_star_stream_take_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:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 
-foo() async {
-  throw 42;
-}
-
-test() async {
-  var exception;
-  try {
-    await foo();
-  } catch (e) {
-    print(await(e));
-    await (exception = await e);
-  }
-  Expect.equals(42, exception);
+mkStream(int n) async* {

[Lasse Reichstein Nielsen, 2015/08/06 12:38:41]

I'd add "Stream" as return type.
Just because checked mode has helped me find bugs in my tests before.

+  for (int i = 0; i < n; i++) yield i;
 }
 
 main() {
+  f(s) async {
+    var r = 0;
+    await for(var v in s.take(5)) r += v;
+    return r;
+  }
+
   asyncStart();
-  test().then((_) => asyncEnd());
+  f(mkStream(10)).then((v) {
+    Expect.equals(10, v);
+    asyncEnd();
+  });
 }
+