Is it necessary to test an Android app with JUnit and Espresso?

i need your opinion in terms of testing an app. I created an app that runs stable and smoothly on my smartphone for weeks, doesn`t that mean that my app will run on other devices stable as well or do i really have to use tools like JUnit and Espresso to test my implementation, or are there other tools you can recommend? I am asking because, i know this tools has their purpose, but obviously my app seems to be stable. Thank you!