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(raw_input())
for _ in range(t):
    n=int(raw_input())
    A=map(int,raw_input().split())
    mx=max(A)
    a=A.index(mx)
    if a!=0:
        print(a)
    else:
        for j in range(1,n):
            if A[j]!=mx:
                print(j-1)
                break
        else:
            print(-1)
        
            
            
        

