#include<stdio.h>
#include<cmath>
#include<algorithm>
#include<iostream>
#include<set>
#include<map>
#include<cstring>
#include<string>
#include<queue>
using namespace std;
char a[1000], b[1000];
int main() {
    int T;
    scanf("%d", &T);
    for (int tt = 0; tt < T; ++tt) {
        int n,m;
        scanf("%d%d", &n,&m);
        set<int> sa[55];
        set<int> tmp;
        for (int i=0;i<m;i++) tmp.insert(i);
        for (int i=0;i<m;i++) sa[i]=tmp;
        for (int i=0;i<n;i++) {
            scanf("%s",a);
            scanf("%s",b);
            set<int> sb[28];
            for (int j=0;j<m;j++) {
                sb[b[j]-'a'].insert(j);
            }
            //puts("===");
            for (int j=0;j<m;j++) {
                for (set<int>::iterator iter = sa[j].begin(); iter != sa[j].end();) {

                    if (sb[a[j]-'a'].count(*iter) == 0) {
                        sa[j].erase(iter++);
                        //iter--;
                    } else iter ++;
                }
                /*
                set<int> tmpp;
                set<int>::iterator iter = tmpp.begin();
                set_intersection(sa[j].begin(), sa[j].end(), sb[a[j]].begin(), sb[a[j]].end(), inserter(tmpp,iter));
                sa[j].swap(tmpp);

                for (set<int>::iterator iter = sa[j].begin(); iter != sa[j].end(); iter++) {
                        cout << j << " " << *iter << endl;
                }*/
            }
        }
        //
        bool succ = true;
        set<int> st;
        vector<int> ans;
        for (int j=0;j<m;j++) {
            int zz = -1;//puts("===");
            for (set<int>::iterator iter = sa[j].begin(); iter != sa[j].end(); ++iter) {
                //    cout << j << " " << *iter << endl;
                if (st.count(*iter)) continue;
                zz = *iter;
                st.insert(zz);
                break;
            }
            if (zz == -1) {
                succ = false;
                break;
            }
            ans.push_back(zz);
        }
        if (succ) {
          // printf("%d\n", ans.size());
            for (int i=0;i<ans.size();++i) {
                printf("%d",ans[i]+1);
                if (i==ans.size()-1) puts("");
                else putchar(' ');
            }
        } else puts("-1");

    }
    return 0;
}