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

import sys


def f(n):
    m = max(n)
    k = 0
    s = -2
    for i in range(len(n)):
        if n[i] == m:
            if i < len(n) - 1 and n[i +1] != m:
                s = i
            if i != 0 and n[i - 1] != m:
                s = i
    return s + 1


# sys.stdin = open('26.txt', 'r', encoding="utf-8")
n = int(input())
for _ in range(n):
    __ = int(input())
    l = list(map(int,input().split()))
    print(f(l))
                
        

