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 _ in range(t):
    n=int(input())
    a=list(map(int,input().split()))
    l=max(a)
    c=a.count(l)
    if n==c:
        print(-1)
    else:
        ind=a.index(l)
        for i in range(ind+1,n-1):
            
            if a[i]<l:
                ind=i
                break
        print(ind)