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

t = int(input())
for case in range(t):
    n = int(input())
    a = [int(x) for x in input().split(' ')]
    if min(a) == max(a):
        ans = -1
    else:
        m = max(a)
        for i in range(n - 1):
            if a[i] != m and a[i + 1] == m:
                ans = i + 2
                break
            elif a[i] == m and a[i + 1] != m:
                ans = i + 1
                break
    print(ans)
