Where to write testcases for mobile apps

I am a tester, but putting my hands on in Android app development and have developed a EdTech app "Class eLearn Mobile app"

As of now, i am manually testing the application and pushing the updates to production.

But now i want to write automated cases in the same development project and implement CI/CD or DevOps. How can we do that? I know in Maven projects, we can have a separate test folder, where we can write functional tests. How can i do the same with Android apps?

Your inputs are highly appreciated.