Can you list the main levels of software testing?

Main levels of software testing:

1. Unit Testing — testing individual components or functions of the program for correctness.
2. Integration Testing — testing the interaction between modules or components.
3. System Testing — testing the entire system as a whole for compliance with requirements.
4. Acceptance Testing — testing the system against user expectations and requirements, often conducted by users.

These levels help identify errors at different stages of development and ensure product quality.