Can you explain the concept of the testing pyramid and its main principles?

The testing pyramid is a concept that describes the optimal ratio of different types of tests in a project to ensure quality effectively. The main idea is to have many low-level automated tests and fewer high-level ones.

Main principles:

• Unit tests (bottom of the pyramid) — the most numerous, fast, and isolated. They test individual functions or methods.
• Integration tests — check the interaction between modules or components.
• E2E (end-to-end) tests (top level) — simulate user behavior and test the entire system, but should be fewer due to complexity and execution time.

This approach helps quickly identify errors early, reduces the cost of fixing bugs, and accelerates feedback for developers.