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

testcases = int(input())

for _ in range(testcases):
    n = int(input())
    l = list(map(int , input().split()))
    if(l.count(l[0]) == n):
        print(-1)
    else:
        m = max(l)
        ans = l.index(m)
        if(ans ==  0):
            while(True):
                if(ans == n-1):
                    break
                if(l[ans] == l[ans+1]):
                    ans+=1     
                    continue
                else:
                    break
        print(ans+1)
        