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);
}