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

from sys import stdin
input = stdin.readline

t = int(input())
for _ in range(t):
    n = int(input())
    a = [int(x) for x in input().split()]
    if len(set(a)) == 1:
        print(-1)
        continue
    m = max(a)
    i = 0
    while a[i] != m or a[i+1] == m:
        i +=1
        if i == n-1: break
    print(i+1)