>>530132413
What you're describing is the central meta-conflict of Undertale. When you beat the game for the first time, you'll get a "neutral" ending and it's expected that you'll feel unsatisfied with it somehow, like you could have done better or done something different. Whether by your own volition or because Flowey tempted you, you'll start again and try to get a "better ending," until you eventually figure out what's best for everyone and achieve True Pacifist.
Maybe you're satisfied and stop playing there. But if you aren't, you'll boot up the game again, and find that the game is ready for you with a question. Are you really satisfied with the "best ending" when you know that the game isn't over and there's more to see and do? Are you really willing to undo all the work you've done just to see what happens if you do something different?
It's not a test, it's just a question. There's no right or wrong answer, it's just asking you to think about what you choose to do. No matter what happens, it's your choice.