anchor.diff:  import 'package:http/src/message.dart';
   
   // "hello,"
  -const HELLO_BYTES = const [104, 101, 108, 108, 111, 44];
  +const _helloBytes = const [104, 101, 108, 108, 111, 44];
   
   // " world"
  -const WORLD_BYTES = const [32, 119, 111, 114, 108, 100];
  +const _worldBytes = const [32, 119, 111, 114, 108, 100];
   
   class _TestMessage extends Message {
     _TestMessage(Map<String, String> headers, Map<String, Object> context, body,
  
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:     });
  
      test("is null for a stream body", () {
        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: const Stream.empty(), headers: {'content-length': '42'});
        expect(request.contentLength, 42);
        expect(request.isEmpty, isFalse);
      });
  