# Codeception Core The most important classes are defined in root of Codeception. * `Codecept` - starts event dispatcher, loads subscribers, starts SuiteManager * `SuiteManager` - starts modules, starts test runner * `TestLoader` - loads tests from files * `Configuration` - loads YAML configuration * `Events` - defines all Codeception events * `TestCase` - applies Codeception feature to `PHPUnit_Framework_TestCase` class.