Covering your code with unit and/or integration tests is not just a sign of high standard of the development process, it's a confidence in the code quality and ability to quickly ensure application stability during framework updates or refactorings. Magento has contributed a lot to cover the framework with these types of tests and create toolkits for the ease of further coverage of custom functionality.
Unit and Integration Testing in Magento 2
Talk by Giancarlo Peris (30 minutes)
A talk about Unit and Integration testing focused on the Magento 2 implementation with some tips/advice from a starter person point of view.