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())
while t:
    t=t-1
    n=int(input())
    a=list(map(int,input().split()))
    m=max(a)
    if a[0]==m:
        s=0
        for i in range(1,n):
            if a[i]!=m:
                s=1
                print(i)
                break
        if s==0:
            print(-1)
    else:
        s=0
        for i in range(1,n):
            if a[i]==m:
                s=1
                print(i+1)
                break
        if s==0:
            print(-1)
        
    
            
