What levels are included in the test pyramid structure?

A testing pyramid typically includes three levels:

1. Unit tests — the lowest and most numerous level. They test individual functions or methods, execute quickly, and are isolated from external dependencies.

2. Integration tests — verify the interaction between components or modules. Slower than unit tests but important for checking connections.

3. E2E (End-to-End) tests — the top level, simulate user behavior, and test the entire system. The slowest and most expensive to maintain.

This approach helps optimize coverage and testing speed, emphasizing fast and reliable unit tests.