使用 react-test-renderer<Switch> 导致“无状态功能组件无法提供参考”警告

Question

I am using react-test-renderer (16.0.0-beta.5) to perform snapshot testing on a custom React Native component. This component contains a Switch component, which causes this warning to be thrown during test execution:

console.error node_modules\\fbjs\\lib\\warning.js:36

Warning: Stateless function components cannot be given refs. Attempts to access this ref will fail.

Check the render method of Switch . in Unknown (created by Switch) in Switch

Minimal code to reproduce:

import React from 'react';
import renderer from 'react-test-renderer';
import { Switch } from 'react-native';

test('renders correctly', () => {
  const tree = renderer.create(
    <Switch />
  );
});

Some more detail: The issue is caused by the native RCTSwitch component used by Switch.render:

return (
  <RCTSwitch
    {...props}
    ref={(ref) => { this._rctSwitch = ref; }}
    onChange={this._onChange}
  />
);

As you can see this component is assigned a ref. However, react-test-renderer uses the following code to check if a component is stateless:

if (typeof value === 'object' && value !== null && typeof value.render === 'function') {
  // Proceed under the assumption that this is a class instance

Because RCTSwitch doesn't have a render method, the warning is raised. Is this a bug?

Answer 1

I added jest.mock('Switch') to the test and now it passes.

Note that doing this removes the Switch component from the snapshot, however since there is no reason to test a pure react-native component I think it's ok as long as all the functions that the Switch uses are tested separately.

Answer 2

Stateless components don't support refs, create a stateful component.

For more detail see this answer