/*
 *
 *         Author:  Dirk Chang (), [email protected]
 *
 * =====================================================================================
 */
 
#include <string>
#include <iostream>
#include <fstream>
#include <algorithm>
#include <set>
#include <iterator>
#include <vector>
using namespace std;
 
class COMP {
private:
	enum Which {NIL, X, Y};
	Which _w;
	size_t _len;
 
public:
	COMP() : _w(NIL), _len(0) {}
	bool operator()(string const &x, string const &y) {
		_len = x.length();
		if(_len > y.length()) {
			_len = y.length();
			_w = Y;
		}
		else if(_len == y.length()) { // eliminate the possibility of x.length() == y.length()
			return x < y;
		}
		else {
			_w = X;
		}
 
		for(size_t i = 0; i < _len; ++i) {
			if(x[i]==y[i]) continue;
			else return x[i] < y[i];
		}
 
		if(_w == X) {
			return y[0] < y[_len];
		}
		else {
			return x[_len] < x[0];
		}
	}
};
 
int main(int argc, char **argv) {
	COMP comp;
	vector<string> *vec;
	string input;
	int n, subn;
 
	ifstream fin(argv[1]);
	fin >> n;
	vec = new vector<string> [n];
	for(int i = 0; i < n; ++i) {
		fin >> subn;
		vec[i].resize(subn);
		for(int j = 0; j < subn; ++j) {
			fin >> vec[i][j];
		}
		sort(vec[i].begin(), vec[i].end(), comp);
		copy(vec[i].begin(), vec[i].end(), ostream_iterator<string>(cout, ""));
		cout << '\n';
	}
 
	delete [] vec;
}