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 t in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    m=max(a)
    i=a.index(m)
    if i==0:
        while 1:
            if a[i+1]<m:
                print(i+1)
                break
            elif a[i+1]==m:
                i+=1
                if i+1==n:
                    print('-1')
                    break
    else:
        print(i+1)            
                  



