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 x in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    b=list(set(a))
    if len(b)==1:
        print(-1)
    else:
        s=max(a)
        t=a[0]
        t1=a[1]
        if t==t1==s:
            i=0
            ans=0
            while i<n:
                if a[i]!=s:
                    print(i)
                    break
                i+=1
        else:
            print(a.index(s)+1)