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 solve(n):
    s=list(map(int,input().split()))
    if len(set(s))==1:
        return -1
    q=max(s)
    for i in range(n):
        if s[i]==q :
            if i!=0 and s[i-1]!=q :
                return i+1
            elif i!=n-1 and s[i+1]!=q :
                return i+1
    

for _ in range(int(input())):
    print(solve(int(input())))

