anchor.diff:      });
   
       test("is null for a stream body", () {
  -      var request = _createMessage(body: new Stream.empty());
  +      var request = _createMessage(body: const Stream.empty());
         expect(request.contentLength, isNull);
       });
   
       test("uses the content-length header for a stream body", () {
         var request = _createMessage(
  -          body: new Stream.empty(), headers: {'content-length': '42'});
  +          body: const Stream.empty(), headers: {'content-length': '42'});
         expect(request.contentLength, 42);
         expect(request.isEmpty, isFalse);
       });
  
positive.code: }
  
  Message _createMessage(
      {Map<String, String> headers,
      Map<String, Object> context,
      body,
      Encoding encoding}) {
    return new _TestMessage(headers, context, body, encoding);
  }
  
  void main() {
    group('headers', () {
  
negative.code:       var controller = new StreamController();
        var request = _createMessage(body: controller.stream);
        expect(request.read().toList(),
            completion(equals([_helloBytes, _worldBytes])));
  
        controller.add(_helloBytes);
        return new Future(() {
          controller
            ..add(_worldBytes)
            ..close();
        });
      });
  
      test("supports a List<int> body", () {
        var request = _createMessage(body: _helloBytes);
        expect(request.read().toList(), completion(equals([_helloBytes])));
      });
  
      test("throws when calling read()/readAsString() multiple times", () {
  