Add a test runner executable.

test/loader_test.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.loader;
 
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 import 'package:unittest/src/loader.dart';
@@ skipping 65 matching lines @@
 
     test("can load and run a failing test", () {
       var liveTest = suite.tests[1].load(suite);
       expectSingleFailure(liveTest);
       return liveTest.run().whenComplete(() => liveTest.close());
     });
 
     test("throws a nice error if the package root doesn't exist", () {
       var loader = new Loader();
       expect(() => loader.loadFile(p.join(_sandbox, 'a_test.dart')),
-          throwsA(isFileSystemException(
+          throwsA(isLoadException(
               "Directory ${p.join(_sandbox, 'packages')} does not exist.")));
     });
   });
 
   group(".loadDir()", () {
     test("ignores non-Dart files", () {
       new File(p.join(_sandbox, 'a_test.txt')).writeAsStringSync(_tests);
       expect(_loader.loadDir(_sandbox), completion(isEmpty));
     });
 
@@ skipping 34 matching lines @@
 
       test("can run tests in those suites", () {
         var suite = suites.firstWhere((suite) => suite.name.contains("a_test"));
         var liveTest = suite.tests[1].load(suite);
         expectSingleFailure(liveTest);
         return liveTest.run().whenComplete(() => liveTest.close());
       });
     });
   });
 }