#include<algorithm>
#include<cassert>
#include<cctype>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<functional>
#include<iomanip>
#include<iostream>
#include<map>
#include<math.h>
#include<queue>
#include<set>
#include<sstream>
#include<stack>
#include<string>
#include<utility>
#include<vector>
using namespace std;

#define ll long long
//#define int ll

const int inf=0x3f3f3f3f;
const ll INF=0x3f3f3f3f3f3f3f3f;

const int MAXLEN = 1000005;
struct SAIS
{
    // 后缀类型
#define L_TYPE 0
#define S_TYPE 1

    int st[MAXLEN];
    int rl[MAXLEN],rk[MAXLEN],lcp[MAXLEN];
    int n;
    //rl:后缀排序后的排名列表,rl[i]代表第i名的后缀的序号
    //rk:名次,rk[i]代表后缀i的名次
    //lcp:height数组,lcp[i]代表列表中第i个后缀和第i-1个后缀的lcp长度

    void init(const string&s,const int&_n)
    {
        n = _n;
        for (int i=1;i<=n;++i) st[i] = s[i-1];
        // st中的字符必须调成正数!!!!!!!!!!!!!!
    }

    // 判断一个字符是否为LMS字符
    inline bool is_lms_char(int *type, int x) {
        return x > 1 && type[x] == S_TYPE && type[x - 1] == L_TYPE;
    }

    // 判断两个LMS子串是否相同
    inline bool equal_substring(int *S, int x, int y, int *type) {
        do {
            if (S[x] != S[y])
                return false;
            x++, y++;
        } while (!is_lms_char(type, x) && !is_lms_char(type, y));

        return S[x] == S[y] && type[x] == type[y];
    }

    // 诱导排序(从*型诱导到L型、从L型诱导到S型)
    // 调用之前应将*型按要求放入SA中
    inline void induced_sort(int *S, int *SA, int *type, int *bucket, int *lbucket,
                             int *sbucket, int nn, int SIGMA) {
        for (int i = 1; i <= nn; i++)
            if (SA[i] > 1 && type[SA[i] - 1] == L_TYPE)
                SA[lbucket[S[SA[i] - 1]]++] = SA[i] - 1;
        for (int i = 0; i <= SIGMA; i++)  // Reset S-type bucket
            sbucket[i] = bucket[i];
        for (int i = nn; i >= 1; i--)
            if (SA[i] > 1 && type[SA[i] - 1] == S_TYPE)
                SA[sbucket[S[SA[i] - 1]]--] = SA[i] - 1;
    }

    // SA-IS主体
    // S是输入字符串，length是字符串的长度, SIGMA是字符集的大小
    int *sais(int *S, int length, int SIGMA) {
        int nn = length;
        assert(S[nn]==0);
        int *type = new int[nn + 5];  // 后缀类型
        int *position = new int[nn + 5];  // 记录LMS子串的起始位置
        int *name = new int[nn + 5];  // 记录每个LMS子串的新名称
        int *SA = new int[nn + 5];  // SA数组
        int *bucket = new int[SIGMA + 5];  // 每个字符的桶
        int *lbucket = new int[SIGMA + 5];  // 每个字符的L型桶的起始位置
        int *sbucket = new int[SIGMA + 5];  // 每个字符的S型桶的起始位置

        // 初始化每个桶
        memset(bucket, 0, sizeof(int) * (SIGMA + 5));
        for (int i = 1; i <= nn; i++)
            bucket[S[i]]++;
        for (int i = 0; i <= SIGMA; i++) {
            if (i==0)
            {
                bucket[i] = bucket[i];
                lbucket[i] = 1;
            }else
            {
                bucket[i] += bucket[i - 1];
                lbucket[i] = bucket[i - 1] + 1;
            }
            sbucket[i] = bucket[i];
        }

        // 确定后缀类型(利用引理2.1)
        type[nn] = S_TYPE;
        for (int i = nn - 1; i >= 1; i--) {
            if (S[i] < S[i + 1])
                type[i] = S_TYPE;
            else if (S[i] > S[i + 1])
                type[i] = L_TYPE;
            else
                type[i] = type[i + 1];
        }
        // 寻找每个LMS子串
        int cnt = 0;
        for (int i = 1; i <= nn; i++)
            if (is_lms_char(type,i))
                position[++cnt] = i;
        // 对LMS子串进行排序
        fill(SA, SA + nn + 3, -1);
        for (int i = 1; i <= cnt; i++)
            SA[sbucket[S[position[i]]]--] = position[i];
        induced_sort(S, SA, type, bucket, lbucket, sbucket, nn, SIGMA);

        // 为每个LMS子串命名
        fill(name, name + nn + 3, -1);
        int lastx = -1, namecnt = 1;  // 上一次处理的LMS子串与名称的计数
        bool flag = false;  // 这里顺便记录是否有重复的字符
        for (int i = 2; i <= nn; i++) {
            int x = SA[i];

            if (is_lms_char(type, x)) {
                if (lastx >= 0 && !equal_substring(S, x, lastx, type))
                    namecnt++;
                // 因为只有相同的LMS子串才会有同样的名称
                if (lastx >= 0 && namecnt == name[lastx])
                    flag = true;

                name[x] = namecnt;
                lastx = x;
            }
        }  // for
        name[nn] = 0;

        // 生成S1
        int *S1 = new int[cnt+5];
        int pos = 0;
        for (int i = 1; i <= nn; i++)
            if (name[i] >= 0)
                S1[++pos] = name[i];
        int *SA1;
        if (!flag) {
            // 直接计算SA1
            SA1 = new int[cnt + 5];

            for (int i = 1; i <= cnt; i++)
                SA1[S1[i]+1] = i;
        } else
            SA1 = sais(S1, cnt, namecnt);  // 递归计算SA1

        // 从SA1诱导到SA
        for (int i = 0; i <= SIGMA; i++) {
            if (i==0)
                lbucket[i] = 1;
            else
                lbucket[i] = bucket[i - 1] + 1;
            sbucket[i] = bucket[i];
        }
        fill(SA, SA + nn + 3, -1);
        for (int i = cnt; i >= 1; i--)  // 这里是逆序扫描SA1，因为SA中S型桶是倒序的
            SA[sbucket[S[position[SA1[i]]]]--] = position[SA1[i]];
        induced_sort(S, SA, type, bucket, lbucket, sbucket, nn, SIGMA);

        delete[] S1;
        delete[] SA1;
        delete[] bucket;
        delete[] lbucket;
        delete[] sbucket;
        delete[] position;
        delete[] type;
        delete[] name;
        // 后缀数组计算完毕
        return SA;
    }

    void build()
    {
        st[0]=st[n+2]=-1;
        st[n+1]=0;
        int SIGMA = 0;
        for (int i=1;i<=n;++i) SIGMA = max(SIGMA,st[i]);
        int * sa = sais(st,n+1,SIGMA);
        for (int i=2;i<=n+1;++i) rk[sa[i]]=i-1;
        delete[] sa;
        for (int i=1;i<=n;++i) rl[rk[i]]=i;
        for (int i=1,len=0;i<=n;++i)
        {
            if (len) --len;
            while (i+len<=n && rl[rk[i]-1]+len<=n && st[i+len]==st[rl[rk[i]-1]+len]) ++len;
            lcp[rk[i]]=len;
        }
    }

#undef L_TYPE
#undef R_TYPE
}sa;
char s[MAXLEN];
char ch[105];
int id[MAXLEN];

void solve()
{
    int n;
    scanf("%d",&n);
    int len=0;
    int minn=inf;
    for(int i=1;i<=n;i++)
    {
        scanf("%s",s+len);
        int k=(int)strlen(s+len);
        for(int j=0;j<k;j++)id[len+j+1]=i;
        len+=k;
        s[len]=ch[i];
        id[len+1]=0;
        len++;
        minn=min(minn,k);
    }
    s[len]='\0';
    sa.init(s,len);
    sa.build();
    int l=0,r=minn;
    while(l<r)
    {
        int mid=(l+r+1)>>1;
        int ck=0;
        for(int i=1;i<=len;i++)
        {
            if(!id[sa.rl[i]])continue;
            int j=i+1;
            vector<int>min_id(n+1,inf),max_id(n+1,0),vis(n+1);
            min_id[id[sa.rl[i]]]=min(min_id[id[sa.rl[i]]],sa.rl[i]);
            max_id[id[sa.rl[i]]]=max(max_id[id[sa.rl[j]]],sa.rl[i]);
            vis[id[sa.rl[i]]]++;
            while(j<=len&&sa.lcp[j]>=mid)
            {
                min_id[id[sa.rl[j]]]=min(min_id[id[sa.rl[j]]],sa.rl[j]);
                max_id[id[sa.rl[j]]]=max(max_id[id[sa.rl[j]]],sa.rl[j]);
                vis[id[sa.rl[j]]]++;
                j++;
            }
            int ckk=1;
            for(int k=1;k<=n;k++)
            {
                if(vis[k]<2||min_id[k]+mid-1>=max_id[k]){ckk=0;break;}
            }
            if(ckk){ck=1;break;}
            i=j-1;
        }
        if(ck)l=mid;
        else r=mid-1;
    }
    printf("%d\n",l);
}

signed main()
{
//  ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);

    for(int i=1;i<=96;i++)ch[i]=(char)i;
    for(int i=97;i<=100;i++)ch[i]=(char)i+26;

    int _;scanf("%d",&_);while(_--)
        solve();
    return 0;
}