Will keep on adding examples/samples about the testing frameworks, as time permits....

 Can check for Awaitility library for writting test classes for Asynchronous code -
 ​https://www.baeldung.com/awaitlity-testing

An article by Martin Fowler worth to visit to understand more about testing -
https://martinfowler.com/articles/practical-test-pyramid.html

Another article -
https://medium.com/@fistsOfReason/testing-is-good-pyramids-are-bad-ice-cream-cones-are-the-worst