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())
    l=list(map(int,input().split()))
    ll=l.copy()
    ll.sort()
    ma=0
    ans=0
    if(ll[0]==ll[len(l)-1]): print(-1)
    else:
        ma=max(l)
        if(l.index(ma)!=0): print(l.index(ma)+1)
        else:
            for i in range(n):
                if(l[i]!=ma):
                    ans=i
                    break
            if(not ans): print(n)
            else:
                print(ans)
            
        
        
