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:   List<String> stackTrace;
  
    TestResult(this.testName, this.expected, this.actual);
  }
  
negative.code:   final int actualPrefixLength = 'Actual: '.length;
    TestResult currentResult;
    Map<String, List<TestResult>> testsByExpectedAndActual =
        <String, List<TestResult>>{};
    Map<String, List<TestResult>> testsByStackTrace =
        <String, List<TestResult>>{};
    while (index < output.length) {
      String currentLine = output[index];
  