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 t in range(int(input())):
    n = int(input())
    # a = list(map(int,input().split()))
    a = [int(j) for j in input().split()]
    if max(a) == min(a):
        print(-1)
    else:
        M = max(a)
        i = a.index(M)
        if i == 0:
            while i < n - 1 and M == a[i+1]:
                i += 1
        print(i+1)