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 find_dominant(fish):
    biggest_size = max(fish)
    for i in range(len(fish)):
        if fish[i] == biggest_size:
            if (i > 0 and fish[i - 1] < biggest_size) or\
                    (i < len(fish) - 1 and fish[i + 1] < biggest_size):
                return i + 1
    return -1


for i in range(int(input())):
    n = input()
    print(find_dominant([int(i) for i in input().split()]))
