code: func ToRetryCount(err error) *retryErr {
  	if retryErr, ok := err.(*retryErr); ok {
  		return retryErr
  	} else {
  		return nil
  	}
  }
docs: // Helper function for testing verification to avoid whitebox testing
  // as well as keeping retryErr as a private.
  // Should NOT be used under any other context.