#include<iostream>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<queue>
#include<set>
#include<map>
#include<string>
#include<cmath>
#include<cstring>
#define QREADTYPE int
using namespace std;
QREADTYPE read(){
	QREADTYPE x = 0 , w = 1;
	char ch = 0;
	while(ch < '0' || ch >'9'){
		if(ch=='-')w=-1;
		ch = getchar();
	}
	while(ch >= '0' && ch <= '9'){
		x = 10 * x + ch -'0';
		ch = getchar();
	}
	return x*w;
}
struct bid{
	int idx;
	int p;
	bool operator<(bid b) const{
		if(p==b.p)
			return idx<b.idx;
		return p<b.p;
	}
}a[200010];
int n,cnt[200010];
void solve(){
	memset(cnt,0,sizeof(cnt));
	n=read();
	for(int i=1;i<=n;++i){
		a[i].idx=i;
		a[i].p=read();
		cnt[a[i].p]++;
	}
	sort(a+1,a+n+1);
	//for(int i=1;i<=n;++i)
	//	printf("idx=%d,p=%d\n",a[i].idx,a[i].p);
	int ans=-1;
	for(int i=1;i<=n;++i){
		if(cnt[a[i].p]==1){
			ans=a[i].idx;
			break;
		}
	}
	printf("%d\n",ans);

}
int main(){
	//freopen("/mnt/c/Users/24115/Documents/io/in.txt","r",stdin);
	//freopen("/mnt/c/Users/24115/Documents/io/out.txt","w",stdout);
	int t=read();
	while(t--)
		solve();
}
