Testing React Native is similar to default React testing, so for a quick intro in React testing - you can check my video tutorial https://www.youtube.com/watch?v=AhH5xFPwNHg.
By default - RN ships with Jest testing library that doesn’t require additional setup and works out of the box. To run tests - use:
npm run test
But default test which can be found in tests/ folder is too simple and for more complicated and useful tests we will require another library - https://github.com/callstack/react-native-testing-library (which replaces Enzyme if you’re familiar with that)
npm install --save-dev @testing-library/react-native
To have more matchers we can also install https://github.com/testing-library/jest-native
npm install --save-dev @testing-library/jest-native
Testing Styled components
!! NOT WORKING in ("jest-styled-components": "7.0.3") !! https://github.com/styled-components/jest-styled-components/issues/294
As styled-components is our RN way of styling - we need to know how to test it. But not now :\
Mocking native modules
Native Modules requires a running React Native application to work properly. In order to use it in tests, you have to provide its separate implementation.
Async storage - https://react-native-community.github.io/async-storage/docs/advanced/jest/#with-jest-setup-file
React Native Gesture Handler - https://docs.swmansion.com/react-native-gesture-handler/docs/#testing
General recommendations about testing
- Test actual result, not state(for example in case of opening/closing modal instead of checking modal state you should check if modal component appeared on the page.)
- In case of testing API request you need to mock the result of the request(you can just copy response from a real request and store it as an object.) and pass it to the component you're testing as a prop.
- For searching elements use
testIDprop on RN component. This is 100% way of finding correct element for your test.
Test project with examples could be found here https://github.com/Hardronox/RN-testing-examples