Add a VmListener and IsolateTest class for running tests in other isolates.

lib/src/remote_exception.dart

Index: lib/src/remote_exception.dart
diff --git a/lib/src/remote_exception.dart b/lib/src/remote_exception.dart
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+// 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.
+
+library unittest.remote_exception;
+
+import 'dart:async';
+
+import 'package:stack_trace/stack_trace.dart';
+
+import 'expect.dart';
+
+/// An exception that was thrown remotely.
+///
+/// This could be an exception thrown in a different isolate, a different
+/// process, or on an entirely different computer.
+class RemoteException implements Exception {
+  /// The original exception's message, if it had one.
+  ///
+  /// If the original exception was a plain string, this will contain that
+  /// string.
+  final String message;
+
+  /// The value of the original exception's `runtimeType.toString()`.
+  final String type;
+
+  /// The value of the original exception's `toString()`.
+  final String _toString;
+
+  /// Serializes [error] and [stackTrace] into a JSON-safe object.
+  ///
+  /// Other than JSON- and isolate-safety, no guarantees are made about the
+  /// serialized format.
+  static serialize(error, StackTrace stackTrace) {
+    var message;
+    if (error is String) {
+      message = error;
+    } else {
+      try {
+        message = error.message.toString();
+      } on NoSuchMethodError catch (_) {
+        // Do nothing.
+      }
+    }
+
+    return {
+      'message': message,
+      'type': error.runtimeType.toString(),
+      'isTestFailure': error is TestFailure,
+      'toString': error.toString(),
+      'stackChain': new Chain.forTrace(stackTrace).toString()
+    };
+  }
+
+  /// Deserializes an exception serialized with [RemoteException.serialize].
+  ///
+  /// The returned [AsyncError] is guaranteed to have a [RemoteException] as its
+  /// error and a [Chain] as its stack trace.
+  static AsyncError deserialize(serialized) {
+    var exception;
+    if (serialized['isTestFailure']) {
+      exception = new RemoteTestFailure._(
+          serialized['message'],
+          serialized['type'],
+          serialized['toString']);
+    } else {
+      exception = new RemoteException._(
+          serialized['message'],
+          serialized['type'],
+          serialized['toString']);
+    }
+
+    return new AsyncError(exception, new Chain.parse(serialized['stackChain']));
+  }
+
+  RemoteException._(this.message, this.type, this._toString);
+
+  String toString() => _toString;
+}
+
+/// A subclass of [RemoteException] that implements [TestFailure].
+///
+/// It's important to preserve [TestFailure]-ness, because tests have different
+/// results depending on whether an exception was a failure or an error.
+class RemoteTestFailure extends RemoteException implements TestFailure {
+  RemoteTestFailure._(String message, String type, String toString)
+      : super._(message, type, toString);
+}