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

def kira(l, n):
    if len(set(l)) == 1:
        return -1
    mx = max(l)
    for i in range(n):
        if l[i] == mx:
            if i != n - 1:
                if l[i + 1] < mx:
                    return i + 1
            if i != 0:
                if l[i - 1] < mx:
                    return i + 1
    return -1

for _ in range(int(input())):
    n = int(input())
    l = list(map(int, input().split()))
    print(kira(l, n))