#include<iostream>
#include<cstdio>
#include<cmath>
#define db double
using namespace std;

int bitmap[1010][1010];
int cont=0, id=0;
void findBit(int inil, int inic, int l, int c){
    int i, j, zero=0, one=0;
    for(i=inil;i<=l;i++){
        for(j=inic;j<=c;j++){
            if(bitmap[i][j]==1) one++;
            else zero++;
        }
    }
    /*cout << endl << "id-> " <<  id << endl;
    for(i=inil;i<=l;i++){
        for(j=inic;j<=c;j++){
            cout << bitmap[i][j];
        }
        printf("\n");
    }
    printf("resp->");*/
    if(zero && one){
        printf("D");
        int lm = (inil+l)>>1;
        int cm = (inic+c)>>1;
        findBit(inil, inic,lm, cm);
        id++;
        findBit(inil, cm+1,lm, c);
        id++;
        findBit(lm+1, inic,l, cm);
        id++;
        findBit(lm+1, cm+1, l, c);
        id++;
        return;
    }else if(one){
        printf("1");
        return;
    }else if(zero){
        printf("0");
        return;
    }else{
        return;
    }
}

int main(){
    int t;
    scanf("%d", &t);
    while(t--){
        int l, c, i, j;
        string s;
        scanf("%d %d", &l, &c);
        for(i=0;i<l;i++){
            cin >> s;
            for(j=0;j<c;j++){
                int conv=s[j]-'0';
                bitmap[i][j]=conv;
            }
        }
        findBit(0,0,l-1,c-1);
        printf("\n");
    }
}