#include <bits/stdc++.h>

using namespace std;

#define forsn(i, s, n) for(int i=s;i<int(n);i++)
#define forn(i, n) forsn(i, 0, n)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define NACHO ios_base::sync_with_stdio(0);cin.tie(NULL);

typedef long long tint;

struct Trie{
    map<char, Trie> arbol;
    bool finPalabra = false;
};

bool encontrado = 1;
string s;
int tamPalabra;

void insertar(Trie &t, int pos) {
    if(pos < tamPalabra){
        if(pos == tamPalabra-1) t.finPalabra = true;
        insertar(t.arbol[s[pos]], pos+1);
    }
}

bool consistent = 1;

void recorrer(Trie &t, const string &palabra){
    if(t.finPalabra && t.arbol.size() > 1){ consistent = 0;}
    for(auto &i:t.arbol) {
        recorrer(i.second, palabra+i.first);
    }
}

int main(){
    NACHO;
    int tc; cin >> tc;
    while(tc--){
        consistent = 1;
        int n; cin >> n;
        Trie t;
        forn(i, n){
            cin >> s;
            tamPalabra = int(s.size())+1;
            insertar(t, 0);
        }
        recorrer(t, "");
        if(consistent) cout << "YES" << "\n";
        else cout << "NO" << "\n";
    }
}
//