What are the main components/levels in the testing pyramid?

The testing pyramid is a concept that describes the optimal ratio of different types of tests to ensure software quality. The main levels of the pyramid:

1. Unit tests

   • Test individual functions or components.
   • Fast, isolated, cover logic.
   • Should constitute the majority of tests.

2. Integration tests

   • Check interaction between modules or services.
   • Slower than unit tests but important for identifying integration issues.

3. System/E2E tests

   • Test the entire application from the user's perspective.
   • The slowest and most expensive to maintain.
   • Used to verify critical scenarios.

Additionally, sometimes the following are distinguished:

• Acceptance tests — verify compliance with requirements.
• Performance and security tests — specialized levels.

The main idea is to have many unit tests, fewer integration tests, and even fewer E2E tests to balance speed, reliability, and coverage.