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())
	arr = list(map(int, input().split()))
	if(len(set(arr)) < 2):
		print(-1)
		continue
	m = max(arr)
	ind = arr.index(m)
	j = ind + 1
	while(j < n and arr[j] == arr[ind]):
		j += 1
	if(j == n and arr[j - 1] == arr[ind]):
		j = ind + 1
	print(j)
