Software testing is conducted at various levels to ensure software quality:
1. Unit Testing: Tests individual components or functions to verify they work as expected. It is usually automated and performed by developers.
2. Integration Testing: Ensures that combined modules or components work together correctly. It identifies interface defects between modules.
3. System Testing: Validates the complete and integrated software system against specified requirements. It includes functional and non-functional testing.
4. Acceptance Testing: Determines whether the system meets business requirements and is ready for deployment. It includes User Acceptance Testing (UAT) and Operational Acceptance Testing (OAT).
Each level serves a specific purpose in the testing process, ensuring the software is robust, functional, and meets user expectations.