>and is another factor to take into account when hiring Chinese people.

I understand what you mean, but it's literally illegal to take any factor into account when hiring Chinese people (literal racism). It's literally a protected status.

Is there some other way to interview and test whether someone will steal your code and send it to China, other than the fact that they're Chinese?

If you can come up with an alternative test you give everyone, it's okay. Using nationality as a shortcut is not OK.