/* -> Written by <-
   -----------
  |K_A_Z_A_M_A|
  |___________|
  |    _    |
  |   (^_^)   |
  |  /( | )\  |
  |____|_|____|
    H O A N G
*/

#define Task ""
#define F first
#define S second
#define push_back pb
#define bit(x, i) (x >> i) & 1
#define inf 1e9 + 7
#define INF 1e18 + 7

#define ckd iml

#include <iostream>
#include <cmath>
#include <vector>
#include <algorithm>
#include <cstring>
#include <iomanip>
#include <string>
#include <sstream>
#include <cstdio>
#include <vector>
#include <set>
#include <queue>
#include <map>
#include <unordered_map>
#include <stack>
#define el "\n"
#define fr(i,a,b) for (int i = (a); i <= (b); ++ i)
#define frr(i,a,b) for (int i = (a); i >= (b); -- i)
#define FR(i, a, b) for (int i = (a); i < (b); ++ i)

using namespace std;

typedef long long ll;
typedef pair <int, int> pii;

const int MOD = 1e9 + 7;
const double eps = 1e-6;
const int maxn = 3e5 + 1;

int n, dd[maxn];
int a[maxn];

void Solve()
{
    cin >> n;
    for (int i = 1; i <= n; ++ i) dd[i] = 0;
    for (int i = 1; i <= n; ++ i){
        cin >> a[i];
        dd[a[i]] ++;
    }
    int res = inf, pos = 0;
    for (int i = 1; i <= n; ++ i)
        if (dd[a[i]] == 1){
            if (res > a[i]){
                res = a[i];
                pos = i;
            }
        }
    if (res == inf)
        cout << -1 << "\n";
    else
        cout << pos << "\n";
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    if(fopen(Task".inp", "r"))
    {
        freopen(Task".inp","r",stdin);
        freopen(Task".out","w",stdout);
    }
    int test_cnt1se = 1;
     cin >> test_cnt1se;
    while (test_cnt1se --)
        Solve();
    return 0;
}
