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

t = input()


def get_result(values):
    maximum = max(values)
    length = len(values)

    for i in range(length):
        bigger_previous = i - 1 >= 0 and values[i - 1] < maximum
        bigger_following = i + 1 < length and maximum > values[i + 1]

        if (values[i] == maximum and (bigger_following or bigger_previous)):
            return i + 1

    return -1


for i in range(t):
    n = input()
    piranhas = map(int, raw_input().split())
    print(get_result(piranhas))
