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 k in range(int(input())):
    a=int(input())
    b=list(map(int,input().split()))
    if len(set(b))==1:
        print(-1)
    else:
        m=max(b)
        for k in range(a-1):
            if b[k]==m and b[k]>b[k+1] :
                print(k+1)
                break
            elif b[k+1]==m and b[k]<b[k+1]:
                print(k+2)
                break
