anchor.diff:        var text = readTextFile(file);
         if (text == textContents) return null;
   
  -      throw new ExpectException(
  +      throw new TestFailure(
             'File $file should contain:\n\n$textContents\n\n'
             'but contained:\n\n$text');
       });
  
positive.code:   Future validate(String dir) {
      return defer(() {
        if (entryExists(path.join(dir, name))) {
          throw new ExpectException('File $name in $dir should not exist.');
        }
      });
    }
  
negative.code:           error.add("  $failure\n");
          }
          completer.completeError(
              new TestFailure(error.toString()), stackTrace);
        }
  
        for (var match in matches) {
  