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(arr, n):
    maxi = max(arr)

    if arr[0] == maxi and arr[0] > arr[1]: return 1

    if arr[n-1] == maxi and arr[n-1] > arr[n-2]: return n

    for i in range(1,n-1):
        if arr[i] == maxi:
            if arr[i] > arr[i-1] or arr[i] > arr[i+1]:
                return i+1
    

    return -1



t = int(input())

for _ in range(t):
    n = int(input())

    arr = list(map(int, input().split()))

    print(solve(arr, n))