//https://www.acwing.com/blog/content/1626/  map用法详解
//https://www.acwing.com/solution/content/55118/  map[数值]=vector<下标序列>
#include<iostream>
#include<map>
#include<vector>
using namespace std;
int main()
{
    int T;
    cin>>T;
    while(T--)
    {
        int n;cin>>n;
        map<int,vector<int> >mp;
        for(int i=1;i<=n;i++)
        {
            int x;cin>>x;
            mp[x].push_back(i);
        }
        int res=-1;
        for(auto it=mp.begin();it!=mp.end();it++)
            if(it->second.size()==1)
            {
                res=it->second[0];
                break;
            }

        cout<<res<<endl;
    }
    return 0;
}