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()))
    m=max(a)
    k=-1
    for j in range(n-1,0,-1):
        if a[j]==m and a[j-1]!=m:
            k=j+1
            break
        elif a[j-1]==m and a[j]!=m:
            k=j
            break
    print(k)