Unit Testing Clean Architecture Use Cases

Unit tests for a Clean Architecture use case should mock every dependency the handler receives and check the Result it returns. The article uses a booking command handler to show how to cover the not-found case, booking overlap, the happy path, and exception propagation with Arrange-Act-Assert and descriptive test names.

It also points out the limit of unit tests when a repository is mocked. A mock can confirm that the handler reacts correctly, but it cannot prove that the real overlap logic works. That part belongs in integration tests with real data.

Reading notes

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• Mock all external dependencies of the handler.
• Use Arrange-Act-Assert and descriptive test names.
• Cover failure paths, the happy path, and exception propagation.
• Mock a date-time provider instead of reading DateTime.UtcNow directly.
• Use unit tests to verify behavior flow, and integration tests to verify real data interactions.
• High code coverage is only a starting point, not proof of good tests.