More gracefully handle load errors.

test/runner/browser/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.
 
 @TestOn("vm")
 
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 import 'package:test/src/backend/state.dart';
@@ skipping 31 matching lines @@
   });
 
   tearDown(() {
     new Directory(_sandbox).deleteSync(recursive: true);
     return _loader.close();
   });
 
   group(".loadFile()", () {
     var suite;
     setUp(() {
-      return _loader.loadFile(p.join(_sandbox, 'a_test.dart')).then((suites) {
+      return _loader.loadFile(p.join(_sandbox, 'a_test.dart')).toList()
+          .then((suites) {
         expect(suites, hasLength(1));
         suite = suites.first;
       });
     });
 
     test("returns a suite with the file path and platform", () {
       expect(suite.path, equals(p.join(_sandbox, 'a_test.dart')));
       expect(suite.platform, equals('Chrome'));
     });
 
@@ skipping 19 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([TestPlatform.chrome]);
     expect(
-        loader.loadFile(p.join(_sandbox, 'a_test.dart'))
+        loader.loadFile(p.join(_sandbox, 'a_test.dart')).first
             .whenComplete(loader.close),
         throwsA(isLoadException(
             "Directory ${p.join(_sandbox, 'packages')} does not exist.")));
   });
 
   test("loads a suite both in the browser and the VM", () {
     var loader = new Loader([TestPlatform.vm, TestPlatform.chrome],
         packageRoot: p.join(packageDir, 'packages'));
     var path = p.join(_sandbox, 'a_test.dart');
-    return loader.loadFile(path).then((suites) {
+    return loader.loadFile(path).toList().then((suites) {
       expect(suites[0].platform, equals('VM'));
       expect(suites[0].path, equals(path));
       expect(suites[1].platform, equals('Chrome'));
       expect(suites[1].path, equals(path));
 
       for (var suite in suites) {
         expect(suite.tests, hasLength(3));
         expect(suite.tests[0].name, equals("success"));
         expect(suite.tests[1].name, equals("failure"));
         expect(suite.tests[2].name, equals("error"));
       }
     }).whenComplete(loader.close);
   });
 }