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 solution(n, arr):
    ans = (-1,0)
    for i in range(1, len(arr)):
        if arr[i-1] != arr[i] and max(arr[i-1],arr[i]) > ans[1]:
            if arr[i] > arr[i-1]:
                ans = (i+1, arr[i])
            else:
                ans = (i, arr[i-1])

    return ans[0]


for _ in range(int(input())): 
    n = int(input())
    a = list(map(int, input().split()))
    print(solution(n, a))
    
    
