ilrein ilrein - 1 month ago 41
React JSX Question

Testing React: Target Container is not a DOM element

I'm attempting to test a React component with Jest/Enzyme while using Webpack.

I have a very simple test @

import React from 'react';
import { shallow } from 'enzyme';

import App from './App';

it('App', () => {
const app = shallow(<App />);
expect(1).toEqual(1);
});


The relative component it's picking up is :

import React, { Component } from 'react';
import { render } from 'react-dom';

// import './styles/normalize.css';

class App extends Component {
render() {
return (
<div>app</div>
);
}
}

render(<App />, document.getElementById('app'));


However, running
jest
causes a failure:

Invariant Violation: _registerComponent(...): Target container is not a DOM element.


With errors @

at Object.<anonymous> (src/App.js:14:48)
at Object.<anonymous> (src/App.test.js:4:38)


The test files references line 4, which is the import of
<App />
, that causes a fail. The stack trace says line 14 of
App.js
is the reason for the failure -- which is nothing more than the render call from
react-dom
, something I've never had a challenge with (the app renders properly from my Webpack setup).

For those interested (Webpack code):

module.exports = {
entry: './src/App',
output: {
filename: 'bundle.js',
path: './dist'
},
module: {
loaders: [
{
test: /\.js?$/,
exclude: /node_modules/,
loader: 'babel',
query: {
presets: ['react', 'es2015']
}
},
{
test: /\.css$/,
loader: 'style!css-loader?modules&importLoaders=1&localIdentName=[name]__[local]___[hash:base64:5]'
},
{
test: /\.scss$/,
loader: 'style!css-loader?modules&importLoaders=1&localIdentName=[name]__[local]___[hash:base64:5]!sass'
}
]
}
}


And my
package.json
:

{
"name": "tic-tac-dux",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"dev": "webpack-dev-server --devtool eval --progress --colors --inline --hot --content-base dist/",
"test": "jest"
},
"jest": {
"moduleNameMapper": {
"^.+\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$": "<rootDir>/__mocks__/fileMock.js",
"^.+\\.(css|sass)$": "<rootDir>/__mocks__/styleMock.js"
}
},
"keywords": [],
"author": "",
"license": "ISC",
"devDependencies": {
"babel-core": "^6.17.0",
"babel-jest": "^16.0.0",
"babel-loader": "^6.2.5",
"babel-polyfill": "^6.16.0",
"babel-preset-es2015": "^6.16.0",
"babel-preset-react": "^6.16.0",
"css-loader": "^0.25.0",
"enzyme": "^2.4.1",
"jest": "^16.0.1",
"jest-cli": "^16.0.1",
"node-sass": "^3.10.1",
"react-addons-test-utils": "^15.3.2",
"react-dom": "^15.3.2",
"sass-loader": "^4.0.2",
"style-loader": "^0.13.1",
"webpack": "^1.13.2",
"webpack-dev-server": "^1.16.2"
},
"dependencies": {
"react": "^15.3.2",
"react-dom": "^15.3.2"
}
}


Oh, and if anyone is going to say that the div element isn't being loaded before the script, here's my
index.html
:

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>App</title>
</head>
<body>
<div id="app"></div>
<script src="/bundle.js"></script>
</body>
</html>


What could be the reason for this peculiar rendering problem? Something to do with a new Jest update to 15.0?

Answer

App.jsx is supposed to export the App class and do nothing more, render should be called elsewhere.

If you remove the render call from the App.jsx error should disappear, it pops up because the test environment doesn't supply the DOM with an app id.