Unit & Integration Testing

This topic covers the full spectrum of testing in software engineering, from isolated unit tests through integration tests that verify real system behavior. All examples use Rust.

Contents

1. Unit Testing Fundamentals — What makes a good unit test, the AAA pattern, test naming, Rust testing mechanics, assert macros, #[should_panic].
2. Test-Driven Development — The Red-Green-Refactor cycle, step-by-step TDD in Rust, when TDD works well and when it is awkward, anti-patterns.
3. Property-Based Testing — Properties vs. examples, proptest in Rust, custom strategies, shrinking, real bugs found by property tests.
4. Mocking and Test Doubles — Stubs, mocks, fakes, spies. Trait-based dependency injection in Rust, the mockall crate, when to mock vs. use real implementations.
5. Integration Testing — Testing with real databases (sqlx test fixtures), API endpoint testing, test containers, test isolation strategies.
6. Code Coverage and Metrics — Line vs. branch vs. function coverage, the coverage trap, useful targets (70-80%), cargo-tarpaulin, nextest.

Diagrams