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 dominant(arr):
    biggest = max(arr)
    for i in range(len(arr)):
        if arr[i] == biggest:
            if i >= 1 and arr[i-1] != biggest or i < len(arr) - 1 and arr[i+1] != biggest:
                return i + 1
    return -1



T = int(input())
for t in range(T):
    n = int(input())
    arr = [int(i) for i in input().split(' ')]
    print(dominant(arr))
