#include <stdio.h>

int main () {
  int t = 0;
  int n = 0;
  int a = 0;
  
  int res = 0;
  
  res = scanf("%d", &t);
  while (t > 0) {
    int ans = 0;
    int prev = 0;
    res = scanf("%d", &n);
    res = scanf("%d", &a);
    prev = a;
    n--;
    while (n > 0) {
      res = scanf("%d", &a);
      if (ans <= prev-a) {
        ans = prev-a+1;
      }
      n--;
    }
    printf("%d\n", ans);
    t--;
  }
  
  return 0;
}