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

t = int(input())
for _ in range(t):
    n = int(input())
    a = list(map(int,input().split())) 
    if len(set(a))==1:
        print (-1)
        continue
    m = max(a)
    a = [m] + a + [m]
    for i in range(1,n+1):
        if a[i]!=m:continue
        if a[i-1]<a[i] or a[i+1]<a[i]:
            print (i)
            break