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())
	# n,k = [int(x) for x in input().split()]
	a = [int(x) for x in input().split()]
	# k = input()
	k = a[0]
	found=False
	b = list(set(a))
	if len(b)==1:
		print(-1)
	else:
		temp=max(a)
		if a[0]==temp:
			for i in range(0,n-1):
				if a[i+1]<temp:
					print(i+1)
					break
		else:
			print(a.index(temp)+1)