public class Main{
static void printBiggest(Vector<String> arr) {
Collections.sort(arr,new Comparator<String>() {
@Override
public int compare(String X, String Y) {
String XY= X + Y;
String YX= Y + X;
return XY.compareTo(YX) >0 ? -1:1;
}
});
for(int i=0;i<arr.size();i++) {
System.out.print(arr.get(i));
}
}
public static void main(String[] args) {
Scanner scn=new Scanner(System.in);
int t=scn.nextInt();
while(t-->0) {
int n=scn.nextInt();
Vector<String> arr=new Vector<>();
for(int i=0;i<n;i++) {
arr.add(scn.next());
}
printBiggest(arr);
}
}
}
