           expectIsType(id, value, 'boolean');
            return /** @type {boolean} */ (value);
        }

        /**
   * As above, but also makes sure that the value is an integer.
   * @param {string} id The key that identifies the desired number.
   * @return {number} The corresponding number value.
   */
        getInteger(id) {
            const value = this.getValue(id);
            expectIsType(id, value, 'number');
            expect(value === Math.floor(value), 'Number isn\'t integer: ' + value