import java.util.*;
public class Main {
public static void main(String args[]) throws Exception{
Scanner sc = new Scanner(System.in);
int t = sc.nextInt();
while(t>0) {
t--;
int n = sc.nextInt();
List<String> a = new ArrayList<String>();
for(int i =0; i<n;i++) {
String a1 = sc.next();
a.add(a1);
}
LargestNumber(a);
}
}
public static void LargestNumber(List<String>a ) {
Collections.sort(a, new Comparator<String>() {
public int compare(String X, String Y) {
String XY = X+Y;
String YX = Y+X;
int comp = XY.compareTo(YX);
if(comp > 0) {
return -1;
}else {
return 1;
}
}
});
Iterator<String> it = a.iterator();
while(it.hasNext()) {
System.out.print(it.next());
}
}
}