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

l = int(input())
while(l):
    p = input()
    n = list(map(int,input().split()))
    m = max(n)
    if(len(n)==sum(n)):
        print("-1")
        break
    for i in range(len(n)):
        if(n[i]==m and n[i+1]!=m):
            print(i+1)
            break
            
        

    l-=1