Unit, integration, mocking, test isolation.
Connects to: CI/CD (Part 23), Database Design (Part 15), and Software Architecture (Part 20).
Create a simple Shopping Cart class. Write tests for adding items, calculating totals with tax, and applying discount codes. Use mocks for an external inventory API.
Apply all concepts from this volume to build a comprehensive feature.
// Example project code hereA stub is a dummy piece of code that lets the test run, returning hardcoded data. A mock is a stub that also records how it was called so you can assert against it later.
Because they rely on the UI structure. If a CSS class or button ID changes, the E2E test fails even if the business logic works perfectly.
Typically by running a clean database instance (like testcontainers). You can either run DB migrations before all tests, and wrap each test in a transaction that rolls back at the end, or truncate all tables between tests.
When the code has no pure logic and is purely wiring (e.g., a controller that just passes data to a service). In those cases, an integration test provides much higher ROI than a unit test with 10 mocks.