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():
    input()
    l = [int(a) for a in input().split()]
    m = max(l)
    if m == min(l):
        return -1
    else:
        s = 0
        for i in range(len(l)):
            if l[i] == m:
                if i > 0:
                    if l[i-1] != m:
                        return i+1
                if i < len(l)-1:
                    if l[i+1] != m:
                        return i+1


for t in range(int(input())):
    print(f())
