Let completers complete in the zone they were constructed in.

tests/standalone/io/async_catch_errors_test.dart

+// Copyright (c) 2013, 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 "package:expect/expect.dart";
+import 'dart:async';
+import 'dart:isolate';
+import 'dart:io';
+
+var events = [];
+
+void testSocketException() {
+  var completer = new Completer();
+  runZonedExperimental(() {
+    Socket.connect("4", 1).then((Socket s) {
+      Expect.fail("Socket should not be able to connect");
+    });
+  }, onError: (err) {
+    if (err is! SocketException) Expect.fail("Not expected error: $err");
+    completer.complete("socket test, ok.");
+    events.add("SocketException");
+  });
+  return completer.future;
+}
+
+void testFileException() {
+  var completer = new Completer();
+  runZonedExperimental(() {
+    new File("lol it's not a file\n").openRead().listen(null);
+  }, onError: (err) {
+    if (err is! FileException) Expect.fail("Not expected error: $err");
+    completer.complete("file test, ok.");
+    events.add("FileException");
+  });
+  return completer.future;
+}
+
+main() {
+  // We keep a ReceivePort open until all tests are done. This way the VM will
+  // hang if the callbacks are not invoked and the test will time out.
+  var timeOutPort = new ReceivePort();
+  testSocketException()

[Anders Johnsen, 2013/07/11 13:43:37]

Just an idea, but you could remove events and change it to

  Future.wait([testSocketException(),
               testFileException()])
      .then((events) { ...});

and let the completer complete with the right value in the correct cases only.

[floitsch, 2013/07/11 14:06:22]

Yes. But frequently I add events at other locations. It allows to trace
execution.

+    .then((_) => testFileException())
+    .then((_) {
+      timeOutPort.close();
+      Expect.listEquals(["SocketException", "FileException"],
+                        events);
+    });
+}