fix for 1.12.0-dev SDK and 0.25.1 analyzer breaking changes

lib/src/testing.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 dev_compiler.src.testing;
 
 import 'dart:collection' show Queue;
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/generated/ast.dart';
@@ skipping 187 matching lines @@
       ErrorSeverity.ERROR: Level.SEVERE,
       ErrorSeverity.WARNING: Level.WARNING,
       ErrorSeverity.INFO: Level.INFO
     }[actual.errorCode.errorSeverity];
   }
 
   String _formatActualError(AnalysisError actual) {
     var span = _createSpan(actual.offset, actual.length);
     var levelName = _actualErrorLevel(actual).name.toLowerCase();
     var msg = span.message(actual.message, color: colorOf(levelName));
-    return '$levelName: $msg';
+    return '$levelName: [${actual.errorCode.name}] $msg';

[Jennifer Messerly, 2015/07/09 17:03:29]

makes it easier to debug

   }
 
   SourceSpan _createSpan(int offset, int len) {
     return createSpanHelper(
         _unit, offset, offset + len, _unit.element.source, _unitSourceCode);
   }
 }
 
 /// Describes an expected message that should be produced by the checker.
 class _ErrorExpectation {
@@ skipping 24 matching lines @@
     expect(tokens[1], "should", reason: 'invalid error descriptor');
     expect(tokens[2], "be", reason: 'invalid error descriptor');
     if (tokens[0] == "pass") return null;
     // TODO(leafp) For now, we just use whatever the current expectation is,
     // eventually we could do more automated reporting here.
     return _parse(tokens[0]);
   }
 
   String toString() => '$level $typeName';
 }