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())
    ar=list(map(int,input().split()))
    prev=0;ans=0
    if len(set(ar))==1:
        print(-1)
    elif ar==sorted(ar):
        for i in range(1,n):
            if ar[i-1]<ar[i]:
                print(i)
                break
    elif ar==sorted(ar,reverse=True):
        for i in range(1,n):
            if ar[i-1]>ar[i]:
                print(i)
                break
    else:
        prev=ar[0]
        for i in range(1,n):
            if ar[i]<prev:
                prev=ar[i]
                ans=i
                break
        print(ans)
