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()))
    k=max(a)
    c=0
    for i in range(n-1):
        if a[i]<k and a[i+1]==k:
            print(i+2)
            c=1
            break
        if a[i]==k and a[i+1]<k:
            print(i+1)
            c=1
            break
    if c==0:
        print(-1)