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())
    a = list(map(int,input().split()))
    max_size=max(a)
    min_size=min(a)
    if(max_size==min_size):
        print(-1)
    else:
        index = a.index(max_size)
        if(index==0):
            for i in range(1,n):
                if a[i]!=max_size:
                    index=i-1
                    break
        print(index+1)