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 i in range(int(input())):
    input()
    l = list(map(int, input().split()))
    if max(l) == min(l):
        print(-1)
    else:
        for i in range(len(l) - 1):
            if(l[i] != max(l) and l[i + 1] == max(l)):
               print(i + 2)
            elif l[i] == max(l) and l[i + 1] != max(l):
                print(i + 1)