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()))
    if(len(set(l))<2):
        print(-1)
    else:
        m=l.index(max(l))
        if(m-1)>-1:
            print(m+1)
        else:
            while m+1<n:
                if l[m+1]!=l[m]:
                    break
                m=m+1
            print(m+1)
