The service locator pattern is a design pattern used in software development to encapsulate the processes involved in obtaining a service with a strong abstraction layer.

We already mention it in our article: How to develop a flexible Apex code for Salesforce.

Testing is the key to successful long-term development and is a critical component of the development process. Unit tests validate that your application works as expected, that there are no unexpected behaviors.

Apex provides a testing framework that allows you to write unit tests, run your tests, check test results, and have code coverage results.