react-navigation-hooks: How to test useFocusEffect

Question

As I understand it should be done so that useFocusEffect would work as useEffect for testing (mock). I use useFocusEffect for fetchData:

useFocusEffect(
  useCallback(() => {
    fetchData();
  }, [fetchData]),
);

Error message: react-navigation hooks require a navigation context but it couldn't be found. Make sure you didn't forget to create and render the react-navigation app container. If you need to access an optional navigation object, you can useContext(NavigationContext), which may return

Package versions:

"jest": "^24.9.0",
"react-native": "0.61.2",
"react-navigation": "^4.0.10",
"react-navigation-hooks": "^1.1.0",
"@testing-library/react-native": "^4.0.14",

Answer 1

Assuming you're rendering your component in your test, you need to wrap it in a fake <NavigationContext>. Doing so lets useFocusEffect look up the things it needs to determine if the component has been focused by your app's navigation.

This example uses render from react-native-testing-library. I think it's analogous to other rendering methods though.

import { NavigationContext } from "@react-navigation/native"
import { render } from "react-native-testing-library"

// fake NavigationContext value data
const navContext = {
  isFocused: () => true,
  // addListener returns an unscubscribe function.
  addListener: jest.fn(() => jest.fn())
}

// MyComponent needs to be inside an NavigationContext, to allow useFocusEffect to function.
const { toJSON } = render(
  <NavigationContext.Provider value={navContext}>
    <MyComponent />
  </NavigationContext.Provider>
)