• In the production code: remove type assertions with as (type assertions are removed at compile-time, there is no runtime checking associated with a type assertion. There won’t be an exception or null generated if the type assertion is wrong). In certain cases as const is acceptable (for example when defining readonly arrays/objects). Using as in tests is tolerable.
• Remove bypass type checking with any (when you want to accept anything because you will be blindly passing it through without interacting with it, you can use unknown). Using any in tests is tolerable.
• Remove non-null assertion operators (just like other type assertions, this doesn’t change the runtime behavior of your code, so it’s important to only use ! when you know that the value can’t be null or undefined).
• Remove all @ts-expect-error and @eslint-disable.
• Remove all warnings, and errors that we are used to ignore (yarn test:lint, yarn test:types, yarn start:web...).
• Use gap (ViewGap) instead of <Spacer.Column />, <Spacer.Row /> or <Spacer.Flex />.
• Don't add new "alias hooks" (hooks created to group other hooks together). When adding new logic, this hook will progressively become more complex and harder to maintain.
• Remove logic from components that should be dumb.

Test specific:

• Avoid mocking internal parts of our code. Ideally, mock only external calls.
• When you see a local variable that is over-written in every test, mock it.
• Prefer user to fireEvent.
• When mocking feature flags, use setFeatureFlags. If not possible, mention which one(s) you want to mock in a comment (example: jest.spyOn(useFeatureFlagAPI, 'useFeatureFlag').mockReturnValue(true) // WIP_NEW_OFFER_TILE in renderPassPlaylist.tsx )
• In component tests, replace await act(async () => {}) and await waitFor(/* ... */) by await screen.findBySomething().
• In hooks tests, use act by default and waitFor as a last resort.
• Make a snapshot test for pages and modals ONLY.
• Make a web specific snapshot when your web page/modal is specific to the web.
• Make an a11y test for web pages.

Advice:

• Use TDD
• Use Storybook
• Use pair programming/mobs