anchor.diff:  import 'package:http/http.dart' as http;
   import 'package:test/test.dart';
   
  +typedef FutureOr<http.StreamedResponse> ServerMockCallback(
  +    http.BaseRequest request, json);
  +
   const String USER_AGENT = 'google-api-dart-client test.client/0.1.0-dev';
   
   class HttpServerMock extends http.BaseClient {
  -  Function _callback;
  +  ServerMockCallback _callback;
     bool _expectJson;
   
  -  void register(Function callback, bool expectJson) {
  +  void register(ServerMockCallback callback, bool expectJson) {
       _callback = callback;
       _expectJson = expectJson;
     }
  
positive.code:           // All errors from the [http.Client] propagate through.
            // We use [TestError] to simulate it.
            httpMock.register(expectAsync2((http.BaseRequest request, string) {
              return new Future.error(new TestError());
            }), false);
          }
  
  
negative.code:       testString(String msg, String expectedBase64) {
          var msgBytes = utf8.encode(msg);
  
          Stream<List<int>> singleByteStream(List<int> msgBytes) {
            var controller = new StreamController<List<int>>();
            for (var byte in msgBytes) {
              controller.add([byte]);
            }
  