Add a Loader class for loading tests from files.

test/utils.dart

 // 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.test.utils;
 
 import 'dart:async';
 import 'dart:collection';
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+import 'package:stack_trace/stack_trace.dart';
 
 import 'package:unittest/src/live_test.dart';
 import 'package:unittest/src/remote_exception.dart';
 import 'package:unittest/src/state.dart';
 import 'package:unittest/unittest.dart';
 
 // The last state change detected via [expectStates].
 State lastState;
 
+final String packageDir = _computePackageDir();
+
+String _computePackageDir() {
+  var trace = new Trace.current();
+  return p.dirname(p.dirname(p.fromUri(trace.frames.first.uri)));
+}
+
 /// Asserts that exactly [states] will be emitted via [liveTest.onStateChange].
 ///
 /// The most recent emitted state is stored in [_lastState].
 void expectStates(LiveTest liveTest, Iterable<State> statesIter) {
   var states = new Queue.from(statesIter);
   liveTest.onStateChange.listen(expectAsync((state) {
     lastState = state;
     expect(state, equals(states.removeFirst()));
   }, count: states.length, max: states.length));
 }
@@ skipping 36 matching lines @@
 /// Returns a matcher that matches a [TestFailure] with the given [message].
 Matcher isTestFailure(String message) => predicate(
     (error) => error is TestFailure && error.message == message,
     'is a TestFailure with message "$message"');
 
 /// Returns a matcher that matches a [RemoteException] with the given [message].
 Matcher isRemoteException(String message) => predicate(
     (error) => error is RemoteException && error.message == message,
     'is a RemoteException with message "$message"');
 
+/// Returns a matcher that matches a [FileSystemException] with the given
+/// [message].
+Matcher isFileSystemException(String message) => predicate(
+    (error) => error is FileSystemException && error.message == message,
+    'is a FileSystemException with message "$message"');
+
 /// Returns a [Future] that completes after pumping the event queue [times]
 /// times.
 ///
 /// By default, this should pump the event queue enough times to allow any code
 /// to run, as long as it's not waiting on some external event.
 Future pumpEventQueue([int times=20]) {
   if (times == 0) return new Future.value();
   // Use [new Future] future to allow microtask events to finish. The [new
   // Future.value] constructor uses scheduleMicrotask itself and would therefore
   // not wait for microtask callbacks that are scheduled after invoking this
   // method.
   return new Future(() => pumpEventQueue(times - 1));
 }