// Working solution to CF 1454B "Unique Bid Auction".
#include <bits/stdc++.h>


using namespace std;


int main(){
int t; cin >> t;


for (int l = 0; l <t ; l++){
    int uniq = 0;
    int n; cin >> n;
int numbers[n];
int uni[n+1] = {};

for(int i =0; i< n; i++){
    cin >> numbers[i];
    uni[numbers[i]]++;
}

for (int j = 0; j<= n; j++){
    if (uni[j] == 1){
        uniq = j;
        break;
    }
}

for(int k = 0; k<n ; k++){
    if(numbers[k] == uniq){
        cout << k+1 << endl;
        break;
    }
}
if (uniq == 0){
    cout << "-1" << endl;
}
    }

}