Add a test runner executable.

test/utils.dart

Index: test/utils.dart
diff --git a/test/utils.dart b/test/utils.dart
index f9b4075d70df066393024421491889b9a0561c3b..64a3da7101a1c4781ad48037ee6d04dfd605ede5 100644
--- a/test/utils.dart
+++ b/test/utils.dart
@@ -8,6 +8,7 @@ import 'dart:async';
 import 'dart:collection';
 
 import 'package:unittest/src/live_test.dart';
+import 'package:unittest/src/load_exception.dart';
 import 'package:unittest/src/remote_exception.dart';
 import 'package:unittest/src/state.dart';
 import 'package:unittest/unittest.dart';
@@ -71,6 +72,11 @@ Matcher isRemoteException(String message) => predicate(
     (error) => error is RemoteException && error.message == message,
     'is a RemoteException with message "$message"');
 
+/// Returns a matcher that matches a [LoadException] with the given [message].
+Matcher isLoadException(String message) => predicate(
+    (error) => error is LoadException && error.innerError == message,
+    'is a LoadException with message "$message"');
+
 /// Returns a [Future] that completes after pumping the event queue [times]
 /// times.
 ///