The classification of the test stages, also called test cycles, follows the complexity: from the individual component to the complex overall system, usually 3 to 4 test stages are defined:
The component test, also called module test or unit test, is a test at the lowest level of the individual modules. The test object is the functionality within individual delimitable parts of the software (modules or units). The test objective of these tests carried out by the software developer is the proof of the technical executability and correct functional (partial) results.
The integration test tests the cooperation of interdependent components. The focus of testing is on the interfaces of the components involved and should prove correct results over complete processes.
The system/web test is the test level at which the entire system is tested against the entire requirements. The test takes place in a test environment and is performed with test data. The test environment should simulate the production environment, i.e. it should be as similar as possible.
The User Acceptance Test (UAT) is the testing of the delivered software by the customer.