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()
    s = list(map(int, input().split()))
    i = s.index(max(s)) + 1
    if i > 1:
        return i
    while i < len(s):
        if s[i - 1] != s[i]:
            return i
        i += 1
    return -1


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