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 max_fish(arr):
    if len(set(arr)) == 1:
        return -1

    best = max(arr)
    for i, fish in enumerate(arr):
        if fish != best:
            continue
        if i - 1 >= 0:
            if arr[i - 1] < fish:
                return i + 1
        if i + 1 <= len(arr) - 1:
            if arr[i + 1] < fish:
                return i + 1


for i in range(int(input())):
    n = input()
    print(max_fish(list(map(int, input().split()))))
