anchor.diff:          }
           if (hasStackTrace) {
             currentResult.stackTrace = output.sublist(index + 1, endIndex - 2);
  +          String traceLine = currentResult.traceLine;
  +          testsByStackTrace
  +              .putIfAbsent(traceLine, () => <TestResult>[])
  +              .add(currentResult);
           }
           index = endIndex;
         }
  
positive.code:       print('  $message');
      }
    }
  }
  
  /// A representation of the result of a single test.
  class TestResult {
    String testName;
    String expected;
    String actual;
  
negative.code:   List<String> stackTrace;
  
    TestResult(this.testName, this.expected, this.actual);
  
    String get traceLine {
      for (int i = 0; i < stackTrace.length; i++) {
        String traceLine = stackTrace[i];
        if (traceLine.startsWith(framePattern) &&
            traceLine.contains('(package:')) {
          return traceLine;
        }
      }
      return null;
    }
  }
  