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


t = int(input())

for _ in range(t):
    n = int(input())
    sizes = list(map(int, input().split()))

    if len(set(sizes)) == 1:
        print(-1)
    else:
        mx = max(sizes)

        if sizes[0] == mx:
            for i in range(n):
                if sizes[i] != mx:
                    print(i)
                    break
        else:
            for i in range(n):
                if sizes[i] == mx:
                    print(i+1)
                    break

