Let’s face it, if you can’t make a pong app for your platform in a few hours then you’re probably not an app developer. If you can’t point at a portfolio of work and/or customers then building a work sample isn’t unheard of.

That said, you will own the finished product (right?!) so add it to your portfolio when finished, eg post screenshots etc on your website.

Be cool about it though, make sure you’re enthusiastic and mention you will be posting the project on github or whatever (if that’s what you do). If they demand they own it then that’s a red flag.

Remember you are also hiring THEM as much as they are hiring you.