/*
枚举+KMP
*/
// include file
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cctype>
#include <ctime>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <bitset>
#include <strstream>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <set>
#include <list>
#include <functional>
using namespace std;
// typedef
typedef long long LL;
typedef unsigned long long ULL;
//
#define read freopen("in.txt","r",stdin)
#define write freopen("out.txt","w",stdout)
#define FORi(a,b,c) for(int i=(a);i<(b);i+=c)
#define FORj(a,b,c) for(int j=(a);j<(b);j+=c)
#define FORk(a,b,c) for(int k=(a);k<(b);k+=c)
#define FORp(a,b,c) for(int p=(a);p<(b);p+=c)
#define FF(i,a) for(int i=0;i<(a);i+++)
#define FFD(i,a) for(int i=(a)-1;i>=0;i--)
#define Z(a) (a<<1)
#define Y(a) (a>>1)
const double eps = 1e-6;
const double INFf = 1e10;
const int INFi = 1000000000;
const double Pi = acos(-1.0);
template<class T> inline T sqr(T a){return a*a;}
template<class T> inline T TMAX(T x,T y)
{
if(x>y) return x;
return y;
}
template<class T> inline T TMIN(T x,T y)
{
if(x<y) return x;
return y;
}
template<class T> inline void SWAP(T &x,T &y)
{
T t = x;
x = y;
y = t;
}
template<class T> inline T MMAX(T x,T y,T z)
{
return TMAX(TMAX(x,y),z);
}
// code begin
#define MAXP 70
#define MAXN 12
char dc[MAXN][MAXP];
int T,N;
char P[MAXP];
int Ps;
int Ts;
int next[MAXP];
char ans[MAXP];
void CalNext()
{
next[0] = 0;
next[1] = 0;
int j;
FORi(2,Ps+1,1)
{
j = next[i-1];
while(true)
{
if(P[j]==P[i-1])
{
next[i] = j+1;
break;
}
if(j==0)
{
next[i]=0;
break;
}
j = next[j];
}
}
}
bool KMP(char T[])
{
Ts = 60;
int i,j;
i = 0; //模式串
j = 0; //文本
while(true)
{
if(j==Ts) break;
if( P[i]==T[j])
{
i++;
j++;
if(i==Ps)
{
return true;
}
}
else if(i>0)
{
i = next[i];
}
else
j++;
}
return false;
}
bool Isok() //判断P是否在其余的N-1个字符串种出现过
{
FORi(1,N,1)
{
if(!KMP(dc[i])) return false;
}
return true;
}
int main()
{
read;
write;
scanf("%d",&T);
while(T--)
{
scanf("%d",&N);
FORi(0,N,1)
{
scanf("%s",dc[i]);
}
strcpy(ans,"zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz");
bool f=false;
// 对第个字符串的长度进行枚举
for(int len=60;len>=3;len--)
{
Ps = len;
for(int i=0;i+len<=60;i++)
{
strncpy(P,dc[0]+i,len);
P[Ps] = 0;
//printf("%d %s\n",len,P);
// 然后做判断
CalNext();
if(Isok())
{
if(strcmp(P,ans)<0)
{
strcpy(ans,P);
f=true;
}
}
}
if(f) break;
}
if(f) printf("%s\n",ans);
else printf("no significant commonalities\n");
}
return 0;
}