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))==1):
        print(-1)
        continue
    a=max(l)
    b=l.index(a)
    j=b+1
    while(j<n and l[j]==l[b]):
        j+=1
    if j==n and l[j-1]==l[b]:
        j=b+1
    print(j)