constructor() {
    /**
     * Time zone offset. For time zones with daylight saving, the different
     * offsets are represented as array of offsets.
     * @private {Array<number>}
     */
    this.timezoneOffset_ = [];
    /**
     * Counter storing the index of next offset value to be returned from the
     * array of offset values.
     * @private {number}
     */
    this.offsetArrayCounter_ = 0;
  }
Mock date class with simplified properties of Date class for testing.