Tell me about the testing pyramid: levels and why is it called a pyramid?

The testing pyramid is a concept that describes the ratio of different levels of tests in a project for effective quality assurance.

Levels of the pyramid:

1. Unit tests — based on testing individual modules or functions. Fast, isolated, cover low-level logic.
2. Integration tests — check the interaction between components or services.
3. E2E tests — simulate user behavior, test the entire system.

Why the pyramid:

• There should be the most unit tests, as they are fast and reliable.
• Fewer integration tests, as they are more complex and slower.
• Even fewer E2E tests, as they are the most resource-intensive and fragile.

This balance helps quickly identify errors early and reduces testing support costs.