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 test():
	n = int(input())
	a = list(map(int,input().split()))
	mx = 0
	for s in a:
		if mx < s:
			mx = s
	for i in range(n):
		if (i!=0 and a[i]==mx and a[i-1]!=mx) or (i!=n-1 and a[i]==mx and a[i+1]!=mx):
			print(i+1)
			return
	print(-1)
		

ttt = int(input())
for i in range(ttt):
	test()
