constructor(locale, style, val, unit, expected, pluralrules) {
    this.locale = locale;
    this.style = style;
    this.val = val;
    this.unit = unit;
    this.expected = expected;
    this.pluralrules = pluralrules;
  }
@param {string} locale
@param {number} style
@param {number} val
@param {string} unit
@param {string} expected
@param {string|undefined} pluralrules