#include<bits/stdc++.h>
using namespace std;
#define pie acos(-1)
#define ll long long
#define pb push_back
#define pf push_front
#define ins insert
#define ppb pop_back
#define ppf pop_front
#define sf(x) double x;scanf("%lf",&x);
#define sc(x) ll x;scanf("%lld",&x);
#define sn(x) scanf("%lld",&x);
#define SORT(a) sort(a.begin(),a.end());
#define REV(a) reverse(a.begin(),a.end());
ll pw(ll x ,ll m){ll mul=1;for(ll i=1;i<=x;i++){mul=mul*2;mul=mul%m;}return mul;}




int main()
{
    sc(t)
    while(t--){
        map<ll,ll>mp,ind;
        sc(n);
        set<ll>st;
        for(ll i=1;i<=n;i++){
            sc(x);
            st.ins(x);
            if(mp[x]){
                ind[x]=0;
                continue;
            }
            ind[x]+=i;
            mp[x]++;
        }
        ll fl=0,in;
        for(auto it=st.begin();it!=st.end();it++){
            if(ind[*it]){
                in=ind[*it];
                fl=1;
                break;
            }
            else fl=0;
        }
        if(fl==0){printf("-1\n");continue;}
        else{
            printf("%lld\n",in);
            continue;

        }
    }
    return 0;
}
