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())
    l=list(map(int,input().split()))
    m=max(l)
    ml=[]
    for i in range(n):
        if(l[i]==m):
            ml.append(i)
    ans=-1
    if(ml[0]!=0):
        ans=ml[0]+1
    else:
        for i in ml:
            if(i!=n-1 and l[i]!=l[i+1]):
                ans=i+1
                break
    print(ans)