#include <map>

#include <set>

#include <list>

#include <cmath>

#include <queue>

#include <stack>

#include <cstdio>

#include <vector>

#include <string>

#include <cctype>

#include <complex>

#include <cassert>

#include <utility>

#include <cstring>

#include <cstdlib>

#include <iostream>

#include <algorithm>

using namespace std;

typedef pair<int,int> PII;

typedef long long ll;

#define lson l,m,rt<<1

#define pi acos(-1.0)

#define rson m+1,r,rt<<11

#define All 1,N,1

#define read freopen("in.txt", "r", stdin)

#define N 100010

const ll  INFll = 0x3f3f3f3f3f3f3f3fLL;

const int INF= 0x7ffffff;

const int mod =  ;

struct Trie{

    int ch[N][];

    int val[N],num;

    void init(){

        num=;

        memset(ch[],,sizeof(ch[]));

    }

    int idx(char c){return c-'';}

    int build(char *s){

        int u=,len=strlen(s),f=;

        for(int i=;i<len;++i){

            int v=idx(s[i]);

            if(!ch[u][v]){

                memset(ch[num],,sizeof(ch[num]));

                val[num]=;

                ch[u][v]=num++;

                f=;

            }

            u=ch[u][v];

            if(val[u]==)return ;

        }

        if(val[u]==)return ;

        val[u]=;

        if(!f)return ;

        return ;

    }

}trie;

int main()

{

    int t,n;

    char str[];

    scanf("%d",&t);

    while(t--){

            trie.init();

        scanf("%d",&n);

        int f=;

        for(int i=;i<n;++i){

            scanf("%s",str);

            if(f){

                f=trie.build(str);

            }

        }

        if(f)printf("YES\n");

        else printf("NO\n");

    }

return ;

}