What types of testing do you know, which ones have you used most often, and what are the differences between them?

There are many types of testing, the main ones are:

• Unit testing — testing individual functions or methods in isolation. Mostly used to verify logic at the code level.
• Integration testing — testing the interaction between multiple modules or components.
• System testing — testing the entire system for compliance with requirements.
• Acceptance testing — testing the system from the user's perspective, often including usage scenarios.
• Regression testing — verifying that new changes haven't broken existing functionality.
• Functional testing — testing functionality according to specifications.
• Non-functional testing — testing performance, security, usability, etc.

Most often, I used unit tests and integration tests, as they allow for quick detection of errors at early stages of development. Unit tests isolate individual parts of the code, while integration tests check their combined operation. For example, a unit test might verify a calculation function, and an integration test might verify interaction with a database.