What types of testing do you know? How do they differ?

There are many types of testing, distinguished by purpose, level, and methods:

• Unit Testing — testing individual functions or methods in isolation from the rest of the system.
• Integration Testing — testing the interaction between modules or components.
• Functional Testing — verifying that the functionality meets the requirements.
• System Testing — testing the entire system in conditions close to real operation.
• Acceptance Testing — checking the system against customer expectations.
• Performance Testing — assessing speed, responsiveness, and stability under load.
• Security Testing — identifying vulnerabilities.
• Regression Testing — ensuring that changes do not break existing functionality.

The differences mainly lie in the scope (from individual functions to the entire system), goals (functionality, performance, security), and methods (automated, manual, load testing).