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

def f(array):
	a = max(array)
	n = len(array)
	for i in range(n):
		if i == 0 and array[i] == a:
			if array[i + 1] != a:
				return i + 1
		elif i == n - 1 and array[i] == a:
			if array[i - 1] != a:
				return i + 1
		elif array[i] == a:
			if array[i - 1] != a:
				return i + 1
			elif array[i + 1] != a:
				return i + 1
	return -1


t = int(input())
for _ in range(t):
	n = int(input())
	piranhas = list(map(int, input().split()))
	out = f(piranhas)
	print(out)
