code: func NewErrorTypeMatcher(t ErrorType) utilerrors.Matcher {
  	return func(err error) bool {
  		if e, ok := err.(*Error); ok {
  			return e.Type == t
  		}
  		return false
  	}
  }
docs: // NewErrorTypeMatcher returns an errors.Matcher that returns true
  // if the provided error is a Error and has the provided ErrorType.