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

for _ in range(int(input())):
    l = int(input())
    ar = list(map(int, input().split()))
    mx = max(ar)
    id = ar.index(mx)
    if (ar.count(mx) == len(ar)):
        print(-1)
    else:
        if (id == 0):
            while (ar[id] == ar[id + 1]):
                id += 1
        print(id + 1)
        