/** @module test-string
 */
declare module "test-string" {
    /**
     * @function
     * @param {string} haystack
     * @param {string|Function|RegExp} tester
     * @returns {boolean} `true` if given `tester` says that given `haystack` matches the conditions
     * @example
     * import testString from "test-string"
     * const result = testString("hello", string => string.startsWith("hell"))
     * result === true
     */
    export default function(haystack: string, tester: string | ((...params: any[]) => any) | RegExp): boolean;
}