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

t=int(input())
for i in range(t):
    n=int(input())
    a=list(map(int,input().split()))
    flag=0
    cur=a[0]
    for i in a:
        if i!=cur:
            flag=1
            break
    else:
        print(-1)
    if flag==1:
        b=a.index(max(a))
        for i in range(b,n-1):
            if a[i]!=a[i+1]:
                print(i+1)
                break
        else:
            print(b+1)