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>0):
    n=  int(input())
    a= [int(i) for i in input().split()]
    if len(set(a))==1:
        print(-1)
    else:
        maxi = max(a)
        for i in range(n):
            if i!=n-1 and (a[i]==maxi and a[i+1]!=maxi):
                print(i+1)
                break
            elif i!=0 and (a[i]==maxi and a[i-1]!=maxi):
                print(i+1)
                break
    t-=1