#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    long long ret = 0, buff, prev;
    cin >> prev;
    for (long long i = 1; i < n; i++) {
      cin >> buff;
      if (buff < prev) {
        ret += prev - buff;
      }
      prev = buff;
    }
    cout << ret << "\n";
  }
  return 0;
}
