Testing & code quality

Commands

yarn test              # run all tests
yarn test:watch        # watch mode
yarn test:coverage     # coverage report
yarn lint              # ESLint
yarn lint:fix          # ESLint with auto-fix
yarn type-check        # TypeScript, no output

Tests

Tests use jest-expo and React Native Testing Library. Native modules like MMKV and expo-secure-store are mocked in jest.setup.ts, so tests run without a native build. @env points to a mock in __mocks__/.

Examples to copy:

Test	Shows
src/shared/utils/__tests__/scale.test.ts	Pure functions
src/features/auth/store/__tests__/useUserStore.test.ts	A Zustand store
src/services/__tests__/utils.test.ts	Pagination helpers
src/shared/utils/__tests__/appLoader.test.ts	The app loader

Redux apps get slice tests, and saga tests if you chose Saga.

import { render, screen } from '@testing-library/react-native';
import Button from '@/shared/components/Button';

it('renders the title', () => {
  render(<Button title="Submit" onPress={() => {}} />);
  expect(screen.getByText('Submit')).toBeOnTheScreen();
});

Put tests in a __tests__/ folder next to the code they test.

ESLint rules that matter

ESLint 9 with flat config, plus a few project rules:

• No deep imports into features. Import @/features/auth, not @/features/auth/store/useUserStore.
• Atomic Zustand selectors. useStore((s) => s.field), never useStore(), which re-renders on every change. Redux apps get a rule requiring the typed useAppDispatch and useAppSelector instead.
• Sorted imports and no unused imports, fixed automatically by yarn lint:fix.
• Prettier formatting runs as an ESLint rule, so one command fixes both.

Git hooks (Husky)

If you kept Husky, these run automatically:

Hook	Does
pre-commit	Blocks direct commits to main or master, runs yarn type-check, and lints the staged files
commit-msg	Checks the message follows Conventional Commits
post-merge	Runs yarn install if yarn.lock changed in the pull

To commit to main on purpose, for example in a solo project, set SKIP_BRANCH_PROTECTION=1.

Commit messages

feat: add biometric login
fix: refresh token race condition
chore: upgrade Expo SDK
docs: explain env setup

feat and fix drive automatic version bumps and changelogs. See EAS builds & releases.