var TEST = function () {  
    
    function _isMatch(str, si, ei) {
        while (si < ei) {
            if (str[si] !== str[ei]) { return false; }
            si++;
            ei--;
        }
        return true;
    }
    
    return {
        doTest: function (str) {
            if (!str) { return ''; }
			
            let len = str.length;
			
            const idx = { s: NaN, e: NaN };
			while (len > 0) {
                idx.s = 0;
                idx.e = len - 1;
				while (str[idx.e]) {
					if (_isMatch(str, idx.s, idx.e)) {
						return str.substring(idx.s, idx.e+1);
					}
					idx.s++;
					idx.e++;
				}
				len--;
			}
            return str[0];
        }
    };
}();