Add a scheduled test library.

pkg/scheduled_test/lib/src/schedule_error.dart

Index: pkg/scheduled_test/lib/src/schedule_error.dart
diff --git a/pkg/scheduled_test/lib/src/schedule_error.dart b/pkg/scheduled_test/lib/src/schedule_error.dart
new file mode 100644
index 0000000000000000000000000000000000000000..0f97161a58a4407f42ea1a8d80f323a117a0498e
--- /dev/null
+++ b/pkg/scheduled_test/lib/src/schedule_error.dart
@@ -0,0 +1,72 @@
+// 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.
+
+library schedule_error;
+
+import 'dart:async';
+
+import 'schedule.dart';
+import 'task.dart';
+import 'utils.dart';
+
+/// A wrapper for errors that occur during a scheduled test.
+class ScheduleError extends AsyncError {
+  /// The schedule during which this error occurred.
+  final Schedule schedule;
+
+  /// The task that was running when this error occurred. This may be `null` if
+  /// there was no such task.
+  final Task task;
+
+  /// Creates a new [ScheduleError] wrapping [error]. The metadata in
+  /// [AsyncError]s and [ScheduleError]s will be preserved.
+  factory ScheduleError.from(Schedule schedule, error, {stackTrace,
+      AsyncError cause, Task task}) {
+    if (error is ScheduleError) {
+      if (schedule == null) schedule = error.schedule;
+      if (task == null) task = error.task;
+    }
+
+    if (error is AsyncError) {
+      // Overwrite the explicit stack trace, because it probably came from a
+      // rethrow in the first place.
+      stackTrace = error.stackTrace;
+      if (cause == null) cause = error.cause;
+      error = error.error;
+    }
+
+    return new ScheduleError(schedule, error, stackTrace, cause, task);
+  }
+
+  ScheduleError(this.schedule, error, stackTrace, AsyncError cause, this.task)
+    : super.withCause(error, stackTrace, cause);
+
+  String toString() {
+    var result = new StringBuffer();
+
+    var errorString = error.toString();
+    if (errorString.contains("\n")) {
+      result.add('ScheduleError:\n');
+      result.add(prefixLines(errorString.trim()));
+      result.add("\n\n");
+    } else {
+      result.add('ScheduleError: "$errorString"\n');
+    }
+
+    result.add('Stack trace:\n');
+    result.add(prefixLines(stackTrace.toString().trim()));
+    result.add("\n\n");
+
+    if (task != null) {
+      result.add('Error detected during task in queue "${task.queue}":\n');
+      result.add(task.generateTree());
+    } else if (schedule.done) {
+      result.add('Error detected after all tasks in the queue had finished.');
+    } else {
+      result.add('Error detected before the schedule started running');
+    }
+
+    return result.toString();
+  }
+}