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 i in range(int(input())):
    n = int(input())
    s = input()
    if len(s.replace(s[:s.index(' ')], '').strip()) == 0:
        print(-1)
    else:
        ip = list(map(int, s.split()))
        m = max(ip)
        for i in range(len(ip)):
            if ip[i] == m and ip[i+1] != m:
                print(i+1)
                break
            if ip[i] != m and ip[i+1] == m:
                print(i+2)
                break
