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())
    l = list(map(int,input().split()))
    if l.count(max(l))==n:
        print('-1')
    else:
        i=j=l.index(max(l))
        while i<=n-2 and l[i]==l[i+1]:
            i+=1
        if i!=n-1:
            print(i+1)
        else:
            print(j+1)