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 solve(n, arr):

    m = max(arr)
    for i in range(1, n):
        if arr[i] == m and arr[i - 1] != m:
            return i + 1
    for i in range(n - 1):
        if arr[i] == m and arr[i + 1] != m:
            return i + 1
    return -1


t = int(input())

while t:
    n = int(input())
    arr = list(map(int, input().split()))
    print(solve(n, arr))
    t -= 1