1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
void solve() {
  int n;
  cin >> n;
  vector<int> v(n);
  for (int i = 0; i < n; i++) cin >> v[i];
  if (max_element(v.begin(), v.end()) == min_element(v.begin(), v.end()))
    cout << -1 << endl;
  else {
    int ans = 0;
    for (int i = 0; i < n - 1; i++)
      if (v[i] < v[i + 1]) {
        ans = i + 2;
        break;
      }
    if (ans == 0) {
      for (int i = 0; i < n - 1; i++)
        if (v[i] > v[i + 1]) {
          ans = i + 2;
          break;
        }
    }
    cout << ans << endl;
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int tt;
  cin >> tt;
  while (tt--) solve();
  return 0;
}
