#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
using namespace std;
void Fast(){
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
}
void File() {
#ifndef ONLINE_JUDGE
    freopen("Input.txt", "r", stdin);
    freopen("Output.txt", "w", stdout);
#endif
}
typedef long long ll;
#define watch(x) cout << (#x) << " = " << x << '\n'
#define endl '\n'
#define all(a)  a.begin(), a.end()
#define fix(n) cout << fixed << setprecision(n)
#define skip continue 
const long double pi = acos(-1);
class vector2{
private:
    float x , y;
};
int main()
{
	Fast();
	int t;cin >> t;
    while(t--){
        int n;cin >> n;
        vector<int>v(n);
        for(auto &it:v){
            cin >> it;
        }
        sort(all(v));
        int cnt = 0 , ans = 0;
        for(int i = n -1 ; i >= 0;i--){
            if(v[i] == v[n-1]){
                cnt++;
                ans = i;
            }
        }
        if(cnt > 2){
            cout << -1 << endl;
        }
        else{
            cout << ans + 1 << endl;
        }
    }
}