#include <stdio.h>
void positionandsort (char x[],char a,char b);

int main()
{
    int count,count1,num,z=0;
    int xxx=0;
    char x[3];
    char a[26]={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','V','Z'};
    char b[26]={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','V','Z'}; 
    scanf("%d",&count);

    while(count>0)
    {   scanf("%d %d",&count1,&num);
        while(num>0)
        {
            scanf("%s",&x);
        positionandsort(a,x[0],x[1]);   


            num -=1;
        }

        while (count1>0)
        {  
            printf("%c",a[z]);

            count1 -=1;
            z +=1;


        }

        printf("\n");
        while (xxx<26)
        {
            a[xxx]=b[xxx];

            xxx +=1; 
            }   
        xxx=0;
        z=0;    
        count -=1;
    }



    return 0;
}

void positionandsort (char x[],char a,char b)
{ int i;
  char j;
    for(i=0;i<26;i++)
    {
        if (x[i]==a){a=i;}
        if (x[i]==b){b=i;}



     } 
    if (a>b){
        j=x[a];
        x[a]=x[b];  
        x[b]=j;
}
 }