The text provides a comprehensive tutorial on setting up continuous integration (CI) for a Yii2 API using CircleCI, with a focus on testing through the Codeception framework. It guides readers through creating a basic API for user authentication, covering steps such as setting up a Yii2 application, configuring a local database, creating Active Record models, and developing a controller to handle registration and login requests. The tutorial emphasizes the importance of testing by detailing how to configure a test environment and write functional tests for the API endpoints using Codeception's suite tools. It also illustrates how to automate the testing process using CircleCI, ensuring that tests run automatically on every change to the API, thereby facilitating efficient development cycles and collaboration among multiple contributors. The tutorial concludes by highlighting the benefits of integrating automated testing and CI in software development, making it possible for teams to maintain and enhance projects effectively.