At what level do you write tests: monolith, microservices? How do you determine the coverage level?

The level of test writing depends on the application's architecture and testing goals. In monolithic applications, unit tests are often written for individual modules and integration tests to verify component interactions. In microservices architecture, the focus shifts to contract tests between services, integration tests, and end-to-end tests to verify business processes.

Test coverage level is determined based on risk analysis and the criticality of functionality. Typically, the aim is to cover key business logic and critical components. Coverage metrics (e.g., code coverage) help assess testing completeness, but it's important not to chase numbers, rather focus on the quality and relevance of tests.

Example approach:

• Unit tests cover individual functions and methods.
• Integration tests verify interaction between modules or services.
• End-to-end tests emulate user scenarios.

This multi-level approach ensures system reliability and robustness.