anchor.diff:            _stderrSubscription.pause();
             _stderrCompleter.complete(null);
           } else {
  -          _testStderr.addAll(encodeUtf8(line));
  -          _testStderr.addAll("\n".codeUnits);
  +          _testStderr.add(encodeUtf8(line));
  +          _testStderr.add("\n".codeUnits);
           }
         });
         _stderrSubscription.pause();
  
positive.code:     var output = createCommandOutput(_command,
                          exitCode,
                          (outcome == "TIMEOUT"),
                          _testStdout,
                          _testStderr,
                          new DateTime.now().difference(_startTime),
                          false);
      assert(_completer != null);
  
negative.code:   }
  
    StreamSubscription _drainStream(Stream<List<int>> source,
                                    OutputLog destination) {
      return source.listen(destination.add);
    }
  
    Map<String, String> _createProcessEnvironment() {
  