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()))
    if len(set(a))==1:
        print("-1")
        continue
    z=max(a) 
    for i in range (n):
        if a[i]!=z:
            continue
        if i>0 and a[i]!=a[i-1]:
            print(i+1)
            break
        if i<n-1 and a[i]!=a[i+1]:
            print(i+1)
            break
    