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())

for ii in range(t):
	n = int(input())

	l = list(map(int, input().split()))

	m = max(l)

	found = False

	for i in l:
		if i != m:
			found = True
			break

	if not found:
		print(-1)

	else:
		found = False
		for i in range(n-1):
			if l[i] == m and l[i+1]!= m:
				found = i
				break

		if not found:
			for i in range(1, n):
				if l[i] == m and l[i-1]!= m:
					found = i
					break

		print(found+1)