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())):
    n = int(input())
    l = list(map(int,input().split()))
    if len(list(set(l))) == 1:
        print(-1)
    elif max(l) == l[0]:
        if l[0] != l[1]:
            print(1)
        else:
            for i in range(n):
                if l[i] != l[0]:
                    print(i)
                    break
    else:
        print(l.index(max(l)) + 1 )