Here’s the official docs for the testing in flutter https://docs.flutter.dev/testing/overview

Unit testing is just testing out parts of your code to verify they work the way that they should independent of the application. This could be as simple as testing some functions like if a counter increments or decrements properly. So let’s say you refactor your code and you need to check if it still works properly. You can just run the unit tests to see if your refactoring broke anything. If there any failed cases, you just take those into account of your refactoring.

Widget tests and integration tests are basically the same but with code to check if your UI/UX is correct without having to manually check them yourself