#include 

char findChar(char keys[], char target){
    char normal[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
	int res;
	for(int i=0;i<26;i++){
        if(keys[i]==target){
            return normal[i];
        }
    }
}

int main(){
    int tc;
    scanf("%d",&tc);
    for(int i=1;i<=tc;i++){
        int n,m,in,index=0;
        scanf("%d %d",&n,&m);
        char keys[n][27];
        char words[m+1];
        char res[m];
        for(int j=0;j