How to mock Picker and Picker.Item with jest in React-Native? - unit-testing

Question

I am trying to snapshot test this snippet of code:
import React, { Component } from 'react';
import {
Picker,
} from 'react-native';
export default class TestComponent extends Component {
render() {
return (
<Picker
selectedValue={this.props.asset.type}
onValueChange={this.props.onTypeChange}>
<Picker.Item label="Type of asset" value="default" />
<Picker.Item label="Car" value="car" />
<Picker.Item label="Boat" value="boat" />
<Picker.Item label="Ship" value="ship" />
</Picker>
);
}
}
My test looks like this right now:
import 'react-native';
import React from 'react';
import TestComponent from './TestComponent';
import renderer from 'react-test-renderer';
describe('TestComponent', () => {
const asset = {
type: 'car',
}
it('renders correctly', () => {
const tree = renderer.create(
<TestComponent
asset={asset} />
).toJSON();
expect(tree).toMatchSnapshot();
});
})
My problem is that I get:
TypeError: Cannot read property '_tag' of undefined
I think that I should mock it based on this issue
I have tried adding simply:
jest.mock('Picker', () => 'Picker')
But than it still throws an error because Picker.Item is still not mocked
Invariant Violation: Element type is invalid: expected a string (for built-
in components) or a class/function (for composite components)
but got: undefined. Check the render method of `TestComponent`.
Other variants I tried with no avail:
jest.mock('Picker', () => {return {Item: 'Item'}});
----------------------------------------------------
class Picker{
Item = 'PickerItem'
}
jest.mock('Picker', () => {
return Picker;
});

Answer 1

Created a github issue as well and here is a working answer:
jest.mock('Picker', () => {
const Picker = class extends Component {
static Item = props => React.createElement('Item', props, props.children);
static propTypes = { children: React.PropTypes.any };
render() {
return React.createElement('Picker', this.props, this.props.children);
}
}
return Picker;
})

Answer 2

For Expo v39, I was able to test #react-native-community/picker by adding the following mock to my test/setup file:
jest.mock('#react-native-community/picker', () => {
const React = require('React')
const RealComponent = jest.requireActual('#react-native-community/picker')
class Picker extends React.Component {
static Item = (props: { children: never }) => {
return React.createElement('Item', props, props.children)
}
render () {
return React.createElement('Picker', this.props, this.props.children)
}
}
Picker.propTypes = RealComponent.propTypes
return {
Picker
}
})
Note that #react-native-community/picker is now react-native-picker/picker.
https://jestjs.io/docs/en/tutorial-react-native#tips