#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <utility>
#include <string>
using namespace std;
vector<int> ret;
vector<vector<int>> adj;
vector<int> indegree;
vector<int> outdegree;
void getEulerCircuit(int cur){
    for( int next = 0 ; next < 26 ; ++next){
        while( adj[cur][next] ){
            adj[cur][next]--;
            getEulerCircuit(next);
        }
    }
    ret.push_back(cur);
}
int main(){
    int c; scanf("%d",&c);
    while(c--){
        ret.clear();
        adj = vector<vector<int>>(26,vector<int>(26));
        outdegree = vector<int>(26);
        indegree = vector<int>(26);
        vector<string> words[26][26];

        int n; scanf("%d",&n);
        for( int i = 0 ; i < n ; ++i ){
            string word; cin >> word;
            adj[word[0]-'a'][word[word.length()-1]-'a']++;
            words[word[0]-'a'][word[word.length()-1]-'a'].push_back(word);
            outdegree[word[0]-'a']++; indegree[word[word.length()-1]-'a']++;
        }
        bool possible = true;
        int plus1 = 0; int minus1 = 0;
        for( int i = 0 ; i < 26 ; ++i ){
            int delta = outdegree[i]-indegree[i];
            if( delta > 1 || delta < -1 ){
                possible = false;
                break;
            }
            if ( delta == 1 ) ++plus1;
            else if( delta == -1 ) ++minus1;
        }
        if( possible ) possible = (plus1 == 1 && minus1 == 1 ) || (plus1 == 0 && minus1 == 0 );

        if( !possible ){
            printf("IMPOSSIBLE\n");
            continue;
        }
        for( int i = 0 ; i < 26 ; ++i ){
            if( outdegree[i] == indegree[i]+1 ){
                int start = i;
//                int dest;
//                for( int j = 0 ; j < 26 ; ++j ){
//                    if(indegree[i] == outdegree[i]+1){
//                        dest = i;
//                        break;
//                    }
//                }
//                adj[dest][start] = true;
                getEulerCircuit(start);
                break;
            }
        }
        if( ret.empty() ){
            for( int i = 0 ; i < 26 ; ++i ){
                if(outdegree[i]){
                    getEulerCircuit(i);
                    break;
                }
            }
        }
        if( ret.size() != n+1 ) printf("IMPOSSIBLE\n");
        else{
            reverse(ret.begin(), ret.end());
            string ans;
            for( int i = 1 ; i < ret.size() ; ++i ){
                if( ans.size() ) ans += " ";
//                if( words[ret[i-1]][ret[i]].empty() ){
//                    ans = "IMPOSSIBLE";
//                    break;
//                }
                ans += words[ret[i-1]][ret[i]].back();
                words[ret[i-1]][ret[i]].pop_back();
            }
            printf("%s\n", ans.c_str());
        }
    }
    return 0;
}