LibTest/async/StreamTransformer/StreamTransformer_A01_t02.dart

// Copyright (c) 2011, 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.

/**
 * @assertion factory StreamTransformer(StreamSubscription<T>
 *   transformer(Stream<S> stream, bool cancelOnError))
 * Creates a StreamTransformer.
 *
 * The returned instance takes responsibility of implementing (bind). When
 * the user invokes bind it returns a new "bound" stream. Only when the user
 * starts listening to the bound stream, the listen method invokes the given
 * closure transformer.
 *
 * @description Checks that [transformer] closure is not invoked until stream
 * is being listened to.
 * @author ilya
 */
import "dart:async";
import "../../../Utils/expect.dart";

main() {
  Stream<int> s = new Stream.fromIterable([1]);
  StreamTransformer<int, dynamic> tr = new StreamTransformer(
    (stream, cancelOnError) {
      Expect.fail('unexpected call to transformer');
      return stream.listen((var x) {});
    }
  );
  s.transform(tr);
}