React Native Quality Control & Assurance 4 — Questions and Answers
Question 1: Which command runs only tests related to files changed since the last git commit in a Jest watch session?
- jest --only-changed
- jest --watchAll
- jest --watch (press 'o') (Correct answer)
- jest --changed-files
Correct answer: jest --watch (press 'o')
In jest --watch mode, pressing 'o' runs only tests related to changed files, speeding up the feedback loop.
Question 2: What is the purpose of the `testID` prop in React Native components?
- It assigns a CSS class for styling in tests
- It provides a stable identifier for automated testing tools to locate elements (Correct answer)
- It marks a component as a unit test target
- It disables the component during test runs
Correct answer: It provides a stable identifier for automated testing tools to locate elements
The testID prop maps to accessibilityIdentifier (iOS) and resource-id (Android), allowing test frameworks to reliably find elements.
Question 3: In React Native, which linting rule helps prevent accessibility issues that would fail QA audits?
- react-native/no-inline-styles
- eslint-plugin-jsx-a11y rules (Correct answer)
- react-native/sort-styles
- no-unused-vars
Correct answer: eslint-plugin-jsx-a11y rules
eslint-plugin-jsx-a11y enforces accessibility best practices at the code level, catching issues before manual QA.
Question 4: When writing a React Native integration test that calls a real API, what is the best practice to avoid test instability?
- Mock the network layer using msw or jest.mock on fetch/axios (Correct answer)
- Use the production API with a test account
- Disable network calls entirely in jest config
- Use real API calls but retry failed tests automatically
Correct answer: Mock the network layer using msw or jest.mock on fetch/axios
Mocking the network layer with tools like msw (Mock Service Worker) or jest.mock keeps tests fast, deterministic, and offline-capable.
Question 5: What does the `--forceExit` flag do when added to a Jest command?
- Forces all tests to pass regardless of result
- Terminates the Jest process after all tests complete even if async operations are still running (Correct answer)
- Skips cleanup between test suites
- Runs tests without coverage collection
Correct answer: Terminates the Jest process after all tests complete even if async operations are still running
--forceExit ensures Jest exits after tests finish even if open handles (like setInterval or unclosed connections) would otherwise keep the process alive.
Question 6: Which Detox method waits for an element to become visible before interacting with it?
- element(by.id('btn')).waitFor().toBeVisible()
- waitFor(element(by.id('btn'))).toBeVisible().withTimeout(5000) (Correct answer)
- expect(element(by.id('btn'))).eventually.toBeVisible()
- await element(by.id('btn')).visible(5000)
Correct answer: waitFor(element(by.id('btn'))).toBeVisible().withTimeout(5000)
Detox's waitFor(element).toBeVisible().withTimeout(ms) polls until the element is visible or the timeout expires.
Question 7: What is Hermes' role in React Native quality assurance?
- It is a test runner for React Native
- It is a JavaScript engine optimized for React Native that improves startup time and reduces memory usage (Correct answer)
- It provides automated crash reporting
- It is a linting tool for React Native code
Correct answer: It is a JavaScript engine optimized for React Native that improves startup time and reduces memory usage
Hermes is a lightweight JavaScript engine built by Meta that improves app start time, memory footprint, and allows bytecode compilation.
React Native Quality Control & Assurance 4
Which command runs only tests related to files changed since the last git commit in a Jest watch session?