Effective Unit Testing

Write isolated unit tests for business logic using the Arrange-Act-Assert pattern.

Differentiate between stubs, fakes, and mocks, and create a mock object to isolate a dependency.

Test asynchronous code within a ViewModel using `XCTestExpectation`.

Apply the Test-Driven Development (TDD) workflow (Red-Green-Refactor) to implement a new function.

Test Combine publishers and subscribers by mocking inputs and verifying outputs.