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 _ in range(int(input())):
    n = int(input())
    x = list(map(int, input().split()))
    s = len(set(x))
    if s == 1:
        print(-1)
    else:
        m = max(x)
        y = x.index(m)
        for i in range(y, n - 1):
            if x[i] != x[i + 1]:
                y = i
                break
        print(y + 1)    