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

import sys
input = sys.stdin.readline
I = lambda : list(map(int,input().split()))

t,=I()
for _ in range(t):
	n,=I()
	l=I()
	x=max(l)
	an=-1
	if l.count(x)!=n:
		for i in range(1,n):
			if l[i-1]!=x and l[i]==x:
				an=i+1;break
		else:
			for i in range(n-1):
				if l[i+1]!=x and l[i]==x:
					an=i+1;break
	print(an)