Unable to test shallow rendering with React Native

[hoangpham95]

Current behavior

I use enzyme 3.10 version to snapshot test with React Native. However, I encounter this error:

this._backHandlerListener = BackHandler.addEventListener("hardwareBackPress", this.handleBackRequested);
                                                               ^

TypeError: Cannot read property 'addEventListener' of undefined
    at SearchBar.componentDidMount SearchBar.tsx:30:49)
    at componentDidMount (/node_modules/enzyme/src/ShallowWrapper.js:429:22)
    at Object.fn [as batchedUpdates] (/node_modules/enzyme-adapter-react-16/src/ReactSixteenAdapter.js:713:16)
    at new batchedUpdates (/node_modules/enzyme/src/ShallowWrapper.js:428:26)
    at Object.shallow (/node_modules/enzyme/src/shallow.js:10:10)

This is the code that cause the crash:

const search = (
    <SearchBar
          cancelSearch={cancelSearchSpy}
          searchApps={searchAppsSpy} />
);
 const wrapper = shallow(search)

Expected behavior

This line of code shouldn't crash the test suite.

Your environment

• macOS Catalina Version 10.15.1
• MacBook Pro (16-inch 2019)
• Processor 2.6 GHz Intel Core i7

API

• shallow
• mount
• render

Version

library	version
enzyme	3.11.0
react	16.8.6
react-dom	N/A
react-test-renderer	N/A
adapter (below)	1.14.0

Adapter

• enzyme-adapter-react-16
• enzyme-adapter-react-16.3
• enzyme-adapter-react-16.2
• enzyme-adapter-react-16.1
• enzyme-adapter-react-15
• enzyme-adapter-react-15.4
• enzyme-adapter-react-14
• enzyme-adapter-react-13
• enzyme-adapter-react-helper
• others ( )

[ljharb]

To test React Native properly, you'd need a React Native adapter (enzyme-adapter-react-16 is for react-dom).

Track #1436 for that.

Specific to your OP, however, the implication is that BackHandler is undefined. Is this something RN provides? If so, you'd have to mock it.

[hoangpham95]

RN is providing this. However I suspect this is a native module. I manage to overcome this bug by mocking BackHandler:

BackHandler.addEventListener = jest.fn(// your function here)

[ljharb]

To test with RN, you'd have to ensure all the RN things are available in node.