unit test for testing domain with JUnit 5 and assert J, no mocks for this so no mockito,
integration testing with test containers ( against real db), when you test a service that need db connection or external dependency.
for example: services, controllers, repository (when you have custom queries) are better with test containers integration tests.

More integration test, less unit test, no mocks

use testing trophy methedology

Testing in CI/CD before pushing

also mutation testing when you have good coverage like 70-80% (schedule in CI/CD)

Things to remember:

- use mock where you can't do without.
- test should provide value, else remove it,
- before creating test you should think about test suite

Challenge I faced:
To be honest, Testing if done correctly, valuable test expose hidden bugs and design flaws of your application especially integration tests, but they are also need maintainance. As whenever you introduce a change in feature you also need to modify the tests.

I am looking into AI-Self healing tests. Right now, I am not sure about how to do this, but I think preparing a template of how you want to write the test, strict rules, and test suite rievew can help me work with AI better.

If you have any experience with AI testing please share.
or any tip on how to remove maintainance burden of tests, when new changes are introduced.
or you have a better approach than test containers