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())
    s=list(map(int,input().split()))
    if len(set(s))==1:
        print(-1)
    else:
        m=max(s)
        for i in range(1,n):
            if s[i]!=s[i-1]:
                if s[i]==m:
                    print(i+1)
                    break
                elif s[i-1]==m:
                    print(i)
                    break