Fix error handling for formatting and update the spec

pkg/analysis_server/test/edit/format_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 test.edit.format;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/edit/edit_domain.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analyzer/src/plugin/plugin_impl.dart';
 import 'package:unittest/unittest.dart' hide ERROR;
 
 import '../analysis_abstract.dart';
+import '../mocks.dart';
 import '../reflective_tests.dart';
 
 main() {
   groupSep = ' | ';
   runReflectiveTests(FormatTest);
 }
 
 @reflectiveTest
 class FormatTest extends AbstractAnalysisTest {
   @override
@@ skipping 54 matching lines @@
       expect(edit.replacement, equals('''
 main() {
   int x = 3;
 }
 '''));
       expect(formatResult.selectionOffset, equals(0));
       expect(formatResult.selectionLength, equals(3));
     });
   }
 
+  Future test_withErrors() {
+    addTestFile('''
+main() { int x = 
+''');
+    return waitForTasksFinished().then((_) {
+      Request request = new EditFormatParams(testFile, 0, 3).toRequest('0');
+      Response response = handler.handleRequest(request);
+      expect(response, isResponseFailure('0'));
+    });
+  }
+
   EditFormatResult _formatAt(int selectionOffset, int selectionLength) {
     Request request = new EditFormatParams(
         testFile, selectionOffset, selectionLength).toRequest('0');
     Response response = handleSuccessfulRequest(request);
     return new EditFormatResult.fromResponse(response);
   }
 }