import java.io.BufferedReader;
import java.io.InputStreamReader;
class FitToPlay{
public static void main(String args[]) throws Exception{
//Scanner s=new Scanner(System.in);
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
int T=Integer.parseInt(br.readLine());
int n=0;
int small=0;
int d2=0;
int d1=0;
int num=0;
for(int i=0;i<T;i++){
n=Integer.parseInt(br.readLine());
String s[]=br.readLine().split(" ");
// for(int k=0;k<n;k++){
// System.out.print(s[k]);
// }
for(int j=0;j<n;j++){
num=Integer.parseInt(s[j]);
if(j==0)
small=num;
else{
d2=num-small;
// System.out.println();
// System.out.println(d2);
if(d2>d1){
d1=d2;
//System.out.print("THE CHANGES"+d2);
}
if(d2<0)
small=num;
}
}
if(d1>0)
System.out.println(d1);
else
System.out.println("UNFIT");
d1=0;
}
}
}