using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
 
namespace Protsyk.Puzzles.StudiousStudent {
    class Program {
        static int N;
 
        static void Main(string[] args) {
            string s = new StreamReader(Console.OpenStandardInput()).ReadToEnd();
            string[] splits = s.Split(new char[] { '\n', '\r' },
                              StringSplitOptions.RemoveEmptyEntries);
 
            N = int.Parse(splits[0]);
            for (int i = 1; i < N + 1; i++) {
                string[] words = splits[i]
                                         .Split(' ')
                                         .Skip(1)
                                         .ToArray();
 
                Console.WriteLine(Solve(words));
            }
        }
 
        private static string Solve(string[] words) {
            string prefix = string.Empty;
            List<string> sorted = new List<string>(words);
 
            while (true) {
                sorted = sorted.OrderBy(x => x).ToList();
                if (sorted.Count == 0) break;
 
                string pr = sorted.First();
                string sf = sorted.Skip(1)
                                .Where(a => a.StartsWith(pr))
                                .Select(s => s.Substring(pr.Length))
                                .Where(s => !string.IsNullOrEmpty(s))
                                .OrderBy(x => x + pr)
                                .FirstOrDefault();
 
                if (string.Compare(pr + pr, pr + sf) < 0)
                    sf = null;
 
                prefix += pr + sf;
                sorted.Remove(pr + sf);
            }
 
            return prefix;
        }
    }
}