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 f(n,arr):
    high=max(arr)
    if arr[0]==high and arr[0]>arr[1]:
        return 1
    if arr[n-1]==high and arr[n-2]<arr[n-1]:
        return n
    for i in range(1,n-1):
        if arr[i]==high:
            if arr[i]>arr[i-1] or arr[i]>arr[i+1]:
                return i+1
    return -1
        


if __name__ == "__main__":
    t=int(input())
    for i in range(t):
        n=int(input())
        arr=list(map(int,input().split()))
        print(f(n,arr))
    pass