#define _CRT_SECURE_NO_DEPRECATE

#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

#include<string>

#include<queue>

#include<vector>

#include<time.h>

#include<cmath>

#include<set>

using namespace std;

typedef long long int LL;

const int MAXN =  *  * ;

int wa[MAXN], wb[MAXN], wv[MAXN], WS[MAXN];

int cmp(int *r, int a, int b, int l)

{

    return r[a] == r[b] && r[a + l] == r[b + l];

}

void da(int *r, int *sa, int n, int m)

{

    int i, j, p, *x = wa, *y = wb, *t;

    for (i = ; i < m; i++) WS[i] = ;

    for (i = ; i < n; i++) WS[x[i] = r[i]]++;

    for (i = ; i < m; i++) WS[i] += WS[i - ];

    for (i = n - ; i >= ; i--) sa[--WS[x[i]]] = i;

    for (j = , p = ; p < n; j *= , m = p)

    {

        for (p = , i = n - j; i < n; i++) y[p++] = i;

        for (i = ; i < n; i++) if (sa[i] >= j) y[p++] = sa[i] - j;

        for (i = ; i < n; i++) wv[i] = x[y[i]];

        for (i = ; i < m; i++) WS[i] = ;

        for (i = ; i < n; i++) WS[wv[i]]++;

        for (i = ; i < m; i++) WS[i] += WS[i - ];

        for (i = n - ; i >= ; i--) sa[--WS[wv[i]]] = y[i];

        for (t = x, x = y, y = t, p = , x[sa[]] = , i = ; i < n; i++)

            x[sa[i]] = cmp(y, sa[i - ], sa[i], j) ? p -  : p++;

    }

    return;

}

int Rank[MAXN], height[MAXN], sa[MAXN];

void calheight(int *r, int *sa, int n){

    int i, j, k = ;

    for (i = ; i <= n; i++) { Rank[sa[i]] = i; }

    for (i = ; i < n; height[Rank[i++]] = k){

        for (k ? k-- : , j = sa[Rank[i] - ]; r[i + k] == r[j + k]; k++);

    }

    return;

}

int r[MAXN], len, n, t, Index[MAXN],vis[MAXN];

char sub[+];

struct Node{

    int cnt,maxsa, minsa;

    void init(){cnt = , maxsa = -, minsa = MAXN;}

}node[];

bool check(int x){

    int tot = ,idx,Lidx;

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

        node[i].init();

    }

    memset(vis, , sizeof(vis));

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

        //heigth[i]是sa[i]和sa[i-1]的LCP

        idx = Index[sa[i]], Lidx = Index[sa[i - ]];

        if (i == len - ){

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

                //判断每个字符串的出现次数和后缀的起始位置的最大值和最小值的差是否不小于x

                if (node[k].cnt >=  && node[k].maxsa - node[k].minsa >= x){

                    tot++;

                }

                node[k].init();

            }

            if (tot == n){ return true; }//n个串都满足要求，说明长度x存在

            tot = ;

            break;

        }

        if (height[i] >= x){

            if (!vis[i]){//每个后缀只算一次

                vis[i] = ; node[idx].cnt++; //记录后缀在该组出现的次数

                node[idx].maxsa = max(node[idx].maxsa, sa[i]);//最大值

                node[idx].minsa = min(node[idx].minsa, sa[i]);//最小值

            }

            if (!vis[i-]){

                vis[i - ] = ; node[Lidx].cnt++;

                node[Lidx].maxsa = max(node[Lidx].maxsa, sa[i-]);

                node[Lidx].minsa = min(node[Lidx].minsa, sa[i-]);

            }

        }

        else{

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

                //判断每个字符串的出现次数和后缀的起始位置的最大值和最小值的差是否不小于x

                if (node[k].cnt >= &&node[k].maxsa-node[k].minsa>=x){

                    tot++;

                }

                node[k].init();

            }

            if (tot == n){ return true;} //n个串都满足要求，说明长度x存在

            tot = ;

        }

    }

    return false;

}

void solve(){

    int L = , R = /, mid, ans = ;

    while (R >= L){

        mid = (L + R) / ;

        if (check(mid)){

            ans = mid;

            L = mid + ;

        }

        else{

            R = mid - ;

        }

    }

    printf("%d\n", ans);

}

int main(){

//#ifdef kirito

//    freopen("in.txt", "r", stdin);

//    freopen("out.txt", "w", stdout);

//#endif

//    int start = clock();

    scanf("%d", &t);

    while (t--){

        scanf("%d", &n); len = ;

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

            scanf("%s", &sub);

            for (int j = ; j < strlen(sub); j++){

                Index[len] = i; //记录每个拼接后每个位置属于原输入的哪个

                r[len++] = (sub[j] - 'a' + n + );

            }

            Index[len] = i;

            r[len++] = val;

        }

        da(r, sa, len, );

        calheight(r, sa, len - );

        solve();

    }

//#ifdef LOCAL_TIME

//    cout << "[Finished in " << clock() - start << " ms]" << endl;

//#endif

    return ;

}