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

for z in range(int(input())):
    n = int(input())
    a = [int(i) for i in input().split()]
    if a.count(a[0]) == n:
        print("-1")
        continue
    ele = max(a)
    index = n
    for i in range(n-1):
        if ele == a[i] and ele != a[i+1]:
            index = i + 1
            break
        if ele != a[i] and ele == a[i+1]:
            index = i + 2
    print(index)
