What types of testing do you know? Briefly, what is each for?

There are several main types of testing:

• Functional testing — checks that the system works according to requirements and performs the necessary functions.
• Non-functional testing — evaluates parameters not related to specific functions, such as performance, security, usability.
• Unit testing — testing individual modules or functions of code to verify their correctness.
• Integration testing — checks the interaction between modules or systems.
• System testing — testing the entire system as a whole.
• Acceptance testing — customer verifies the system against requirements.
• Regression testing — checks that code changes haven't broken existing functionality.
• Performance testing — measures speed, load, and system stability.
• Security testing — identifies vulnerabilities and checks data protection.

Each type is necessary to ensure quality at different stages of software development and operation.