1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

t = int(input())

for _ in range(t):
    n = int(input())
    fish = list(map(int, input().split()))
    fish = dict(map(lambda idx: (idx + 1, fish[idx]), range(n)))
    
    ans = -1
    if len(set(fish)) > 1:
        ans = max(fish, key=lambda x: fish[x])
    
    print(ans)