Functional tests for Ionic4

I have an app in production that we change daily.
Sometimes happens that a working functionality is broken by the last modifications.
I’m looking for a tool to create functional tests that can be run before publishing the app to avoid the problem.
Many features can be tested only using the app and unit tests can’t help in this.

Do you know if there are tools or frameworks that can be used for this purpose?
We often hear about “continuous integration”, “DevOps” and “continuous delivery” but are these paradigms applicable to Ionic?

Thank you very much for your opinion and your suggestions.