#include <bits/stdc++.h>
#define int int64_t

using namespace std;

string compare(const string& a, string b)
{
    sort(b.begin(), b.end(), greater<>());
    if(a > b)
        return "-1";
    multiset<char> can_use;
    for(auto i: b)
        can_use.insert(i);
    string ret;
    for(int i = 0; i < a.size(); i++){
        if(can_use.lower_bound(a[i]) == can_use.end()){
            do {
                can_use.insert(ret.back());
                ret.pop_back();
                i--;
            }while(can_use.upper_bound(a[i]) == can_use.end());
            ret.push_back(*can_use.upper_bound(a[i]));
            can_use.erase(can_use.upper_bound(a[i]));
            break;
        }
        ret.push_back(*can_use.lower_bound(a[i]));
        can_use.erase(can_use.lower_bound(a[i]));
        if(ret[i] != a[i])
            break;
    }
    while(!can_use.empty()){
        ret.push_back(*can_use.begin());
        can_use.erase(can_use.begin());
    }
    if(a >= ret)
        swap(ret.back(), ret[ret.size() - 2]);
    return ret;
}

int32_t main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
    int q;
    cin >> q;
    while(q--){
        int n;
        cin >> n;
        string prev;
        cin >> prev;
        sort(prev.begin(), prev.end());
        bool good = true;
        while(n-- > 1)
        {
            string now;
            cin >> now;
            now = compare(prev, now);
            if(now == "-1")
            {
                good = false;
                break;
            }
            prev = now;
        }
        if(!good)
            cout << "NO" << endl;
        else
            cout << "YES" << endl;
    }
}