将所有字符串插入 trie 中
接着对每个字符串执行查询，遍历 $str[1\cdots n-1]$，如果 trie 中表示某个字符的节点 $p$，$vis(p) \neq 0$
那么就互为前缀

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <queue>
#include <vector>
#include <stack>
#include <map>
#include <set>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <bitset>
#include <assert.h>
#include <unordered_map>

using namespace std;
typedef long long ll;

#define Cmp(a, b) memcmp(a, b, sizeof(b))
#define Cpy(a, b) memcpy(a, b, sizeof(b))
#define Set(a, v) memset(a, v, sizeof(a))
#define debug(x) cout << #x << ": " << x << endl
#define _forS(i, l, r) for(set<int>::iterator i = (l); i != (r); i++)
#define _rep(i, l, r) for(int i = (l); i <= (r); i++)
#define _for(i, l, r) for(int i = (l); i < (r); i++)
#define _forDown(i, l, r) for(int i = (l); i >= r; i--)
#define debug_(ch, i) printf(#ch"[%d]: %d\n", i, ch[i])
#define debug_m(mp, p) printf(#mp"[%d]: %d\n", p->first, p->second)
#define debugS(str) cout << "dbg: " << str << endl;
#define debugArr(arr, x, y) _for(i, 0, x) { _for(j, 0, y) printf("%c", arr[i][j]); printf("\n"); }
#define _forPlus(i, l, d, r) for(int i = (l); i + d < (r); i++)
#define lowbit(i) (i & (-i))
#define MPR(a, b) make_pair(a, b)

pair<int, int> crack(int n) {
    int st = sqrt(n);
    int fac = n / st;
    while (n % st) {
        st += 1;
        fac = n / st;
    }

    return make_pair(st, fac);
}

inline ll qpow(ll a, int n) {
    ll ans = 1;
    for(; n; n >>= 1) {
        if(n & 1) ans *= 1ll * a;
        a *= a;
    }
    return ans;
}

template <class T>
inline bool chmax(T& a, T b) {
    if(a < b) {
        a = b;
        return true;
    }
    return false;
}

ll gcd(ll a, ll b) {
    return b == 0 ? a : gcd(b, a % b);
}

ll ksc(ll a, ll b, ll mod) {
    ll ans = 0;
    for(; b; b >>= 1) {
        if (b & 1) ans = (ans + a) % mod;
        a = (a * 2) % mod;
    }
    return ans;
}

ll ksm(ll a, ll b, ll mod) {
    ll ans = 1 % mod;
    a %= mod;

    for(; b; b >>= 1) {
        if (b & 1) ans = ksc(ans, a, mod);
        a = ksc(a, a, mod);
    }

    return ans;
}

template <class T>
inline bool chmin(T& a, T b) {
    if(a > b) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
bool lexSmaller(vector<T> a, vector<T> b) {
    int n = a.size(), m = b.size();
    int i;
    for(i = 0; i < n && i < m; i++) {
        if (a[i] < b[i]) return true;
        else if (b[i] < a[i]) return false;
    }
    return (i == n && i < m);
}

// ============================================================== //

const int maxn = 1500000 + 10;
const int N = 1e5 + 10;
int n;
char str[N][15];

class Trie {
public:
    int t[maxn][10];
    int vis[maxn];
    int tot;
    Trie() {
        tot = 1;
        memset(t, 0, sizeof t);
        memset(vis, 0, sizeof vis);
    }
    void clear() {
        tot = 1;
        memset(t, 0, sizeof t);
        memset(vis, 0, sizeof vis);
    }

    void insert(const char *str) {
        int p = 1, len = strlen(str);
        for (int i = 0; i < len; i++) {
            int c = str[i]-'0';
            if (!t[p][c]) t[p][c] = ++tot;
            p = t[p][c];
        }
        vis[p]++;
    }

    bool query(const char *str) {
        int p = 1, len = strlen(str);
        for (int i = 0; i < len-1; i++) {
            int c = str[i]-'0';
            p = t[p][c];
            if (vis[p]) return false;
        }
        return true;
    }

} trie;

int main() {
    freopen("input.txt", "r", stdin);
    int T;
    cin >> T;
    while (T--) {
        trie.clear();
        scanf("%d", &n);

        for (int i = 0; i < n; i++) {
            scanf("%s", str[i]);
            trie.insert(str[i]);
        }

        bool ok = true;
        for (int i = 0; i < n; i++) {
            if (trie.query(str[i]) == false) {
                ok = false;
                break;
            }
        }
        ok == true ? puts("YES") : puts("NO");
    }
}