Implement Robust Testing Patterns and Utilities

Covers a testing philosophy and concrete utilities for React Native/Jest test suites. Testing philosophy: TDD (write a failing test first, implement minimal code to pass, refactor after green, never write production code without a failing test) and behavior-driven testing (test public APIs and business requirements, not implementation details, with descriptive behavior-based test names). The factory pattern creates getMockX(overrides?: Partial<X>) functions with sensible defaults and overridable properties to keep tests DRY - shown for both component-props factories and data factories (for example a getMockUser returning a typed User with id/name/email/role, overridable per test).

A custom renderWithTheme render function wraps components with required providers (shown wrapping @testing-library/react-native's render in a ThemeProvider) so tests don't repeat provider setup. Mocking patterns cover whole-module mocks (jest.mock('utils/analytics')), factory-function mocks, accessing a mock via jest.requireMock, and mocking generated GraphQL hooks (useGetItemsQuery) with mockReturnValue. Test structure nests describe blocks by concern (Rendering, User interactions, Edge cases) with beforeEach(() => jest.clearAllMocks()). Query patterns distinguish getByText (must exist), queryByText (may not exist, returns null), and findByText inside waitFor (appears asynchronously). User-interaction tests use fireEvent.changeText/fireEvent.press followed by waitFor to assert an async callback fired.

# Run all tests
npm test

# Run with coverage
npm run test:coverage

# Run specific file
npm test ComponentName.test.tsx

Two anti-patterns are flagged with before/after examples: asserting a mock was called instead of asserting the resulting rendered behavior, and inlining ad hoc, inconsistent test data instead of using a factory (shown causing a missing-field bug when one test's inline object omits a required property). A worked user-interaction example fills in a LoginForm's email and password fields with fireEvent.changeText, presses the login button with fireEvent.press, then asserts the onSubmit callback fired inside waitFor to account for the async submit.

Use it when writing or reviewing React Native/Jest test suites and you need TDD discipline, reusable mock-data factories, provider-aware render helpers, or GraphQL-hook mocking patterns.

Best practices: always use factory functions for props and data, test behavior not implementation, use descriptive test names, organize with describe blocks, clear mocks between tests, and keep one behavior per test.

Works with a react-ui-patterns skill to test all UI states (loading, error, empty, success), and with a systematic-debugging skill by writing a reproducing test before fixing a bug.

Frontend engineers writing or reviewing React Native test suites who want a consistent factory-based approach to mock data and provider setup, and a checklist of common testing anti-patterns to avoid.