Add an [immediate] argument to StreamQueue.cancel.

test/stream_queue_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 filevents.
 
 import "dart:async";
 
 import "package:async/async.dart" show StreamQueue;
 import "package:test/test.dart";
 
 import "utils.dart";
@@ skipping 315 matching lines @@
       await flushMicrotasks();
       expect(lastEvent, 3);
 
       var cancelFuture = subscription.cancel();
       expect(controller.hasListener, isFalse);
       cancel.complete(42);
       expect(cancelFuture, completion(42));
     });
   });
 
-  group("close operation", () {
+  group("cancel operation", () {
     test("closes the events, prevents any other operation", () async {
       var events = new StreamQueue<int>(createStream());
       await events.cancel();
       expect(() => events.next, throwsStateError);
       expect(() => events.skip(1), throwsStateError);
       expect(() => events.take(1), throwsStateError);
       expect(() => events.rest, throwsStateError);
       expect(() => events.cancel(), throwsStateError);
     });
 
     test("cancels underlying subscription, returns result", () async {
       var cancelFuture = new Future.value(42);
       var controller = new StreamController(onCancel: () => cancelFuture);
       var events = new StreamQueue<int>(controller.stream);
       controller.add(1);
       expect(await events.next, 1);
       expect(await events.cancel(), 42);
     });
+
+    group("with immediate: true", () async {
+      test("closes the events, prevents any other operation", () async {
+        var events = new StreamQueue<int>(createStream());
+        await events.cancel(immediate: true);
+        expect(() => events.next, throwsStateError);
+        expect(() => events.skip(1), throwsStateError);
+        expect(() => events.take(1), throwsStateError);
+        expect(() => events.rest, throwsStateError);
+        expect(() => events.cancel(), throwsStateError);
+      });
+
+      test("cancels the underlying subscription immediately", () async {
+        var controller = new StreamController();
+        controller.add(1);
+
+        var events = new StreamQueue<int>(controller.stream);
+        expect(await events.next, 1);
+        expect(controller.hasListener, isTrue);
+
+        events.cancel(immediate: true);
+        await expect(controller.hasListener, isFalse);
+      });
+
+      test("closes pending requests", () async {
+        var events = new StreamQueue<int>(createStream());
+        expect(await events.next, 1);
+        expect(events.next, throwsStateError);
+        expect(events.hasNext, completion(isFalse));
+
+        await events.cancel(immediate: true);
+      });
+
+      test("returns the result of closing the underlying subscription",
+          () async {
+        var controller = new StreamController(
+            onCancel: () => new Future.value(42));
+        var events = new StreamQueue<int>(controller.stream);
+        expect(await events.cancel(immediate: true), 42);
+      });
+
+      test("listens and then cancels a stream that hasn't been listened to yet",
+          () async {
+        var wasListened = false;
+        var controller = new StreamController(
+            onListen: () => wasListened = true);
+        var events = new StreamQueue<int>(controller.stream);
+        expect(wasListened, isFalse);
+        expect(controller.hasListener, isFalse);
+
+        await events.cancel(immediate: true);
+        expect(wasListened, isTrue);
+        expect(controller.hasListener, isFalse);
+      });
+    });
   });
 
-
   group("hasNext operation", () {
     test("true at start", () async {
       var events = new StreamQueue<int>(createStream());
       expect(await events.hasNext, isTrue);
     });
 
     test("true after start", () async {
       var events = new StreamQueue<int>(createStream());
       expect(await events.next, 1);
       expect(await events.hasNext, isTrue);
@@ skipping 255 matching lines @@
     controller.add(4);
     await flushMicrotasks();
     controller.close();
   }();
   return controller.stream;
 }
 
 Stream<int> createLongStream(int eventCount) async* {
   for (int i = 0; i < eventCount; i++) yield i;
 }