How to test Apps functionalities?

Hi community,
I have an app, in which users can edit one of several tables. After editing a backend workflow is triggered, which updates the edited table and also performs a historization-operation of another table.

Now I want to test my implementation. For that I would now go to the app and as a user test all different scenarios of what a user can do in the app. Afterwards I would check after each scenario if the tables in the ONE DATA backend are generated correctly and if the correct error messages are displayed in the app (depending on the scenario).

Is there a way to automate that? How do you test your big complicated apps before releasing them to the customer and ensure that nothing breaks when adding new functionality?

Thanks in advance,
Christoph