Run pub tests against older versions of barback.

third_party/pkg/barback-0.13.0/test/logger_test.dart

 // Copyright (c) 2013, 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 barback.test.logger_test;
 
 import 'package:barback/barback.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import 'utils.dart';
@@ skipping 32 matching lines @@
       [new TransformerGroup([[transformer]])]
     ]});
 
     updateSources(["app|foo.txt"]);
     buildShouldLog(LogLevel.ERROR, equals("This is an error."));
     buildShouldLog(LogLevel.WARNING, equals("This is a warning."));
     buildShouldLog(LogLevel.INFO, equals("This is info."));
     buildShouldLog(LogLevel.FINE, equals("This is fine."));
   });
 }