constructor() {
    /**
     * @type {*} The value to use in test.
     */
    this.value;
    /**
     * @type {*} The expected value.
     */
    this.expectedValue;
    /**
     * @type {string|undefined} The expected text value. Provided if different
     *    from String(expectedValue).
     */
    this.expectedText;
    /**
     * @type {!RegExp|string|undefined} The optional error message matcher.
     *    Provided if test case is expected to throw.
     */
    this.errMsgMatcher;
  }
Class for a field value test case.