Jest fails because Target container is not a DOM element

Issue

I am trying to run component test on React app with jest and failing with below error. But the application is working fine normally

 FAIL  src/__tests__/app.test.tsx
  ● Test suite failed to run

    Target container is not a DOM element.

       7 | import reportWebVitals from './reportWebVitals';
       8 |
    >  9 | ReactDOM.render(
         |          ^
      10 |     <React.StrictMode>
      11 |         <Provider store={store}>
      12 |             <App />

      at Object.render (node_modules/react-dom/cjs/react-dom.development.js:26091:13)
      at Object.<anonymous> (src/index.tsx:9:10)
      at Object.<anonymous> (src/App.tsx:6:1)
      at Object.<anonymous> (src/__tests__/app.test.tsx:45:1)

Here is my App.tsx file.

import React from 'react';
import 'reflect-metadata';
import { BrowserRouter, Switch } from 'react-router-dom';
import { Message } from '@library/queues';

const App: React.FC = () => {
   return (
     <ThemeProvider theme={'dark'}>
      // routes
     </ThemeProvider>
   )}

export default App;

Here is index file

import React from 'react';
import ReactDOM from 'react-dom';
import './index.scss';
import App from 'App';
import { Provider } from 'react-redux';
import store from 'redux/store';
import reportWebVitals from './reportWebVitals';

ReactDOM.render(
    <React.StrictMode>
        <Provider store={store}>
            <App />
        </Provider>
    </React.StrictMode>,
    document.getElementById('root'),
);

// If you want to start measuring performance in your app, pass a function
// to log results (for example: reportWebVitals(console.log))
reportWebVitals();

and finally the test file

import React from 'react';
import { render, screen } from '@testing-library/react';
import App from './App';

test('renders learn react link', () => {
    render(<App />);
    const linkElement = screen.getByText(/learn react/i);
    expect(linkElement).toBeInTheDocument();
});

I have verified many links and tried different ways but all leads to this error only. I am using one private npm module and mapped that using moduleNameMappers and sometimes that also throws error.

moduleNameMapper: {
        '^@library/queues(.*)$': '<rootDir>/src/$1', -- working without errors but throwing errors when we run tests
        // '^@library/queues(.*)$': '<rootDir>/node_modules/$1', -- throwing errors
        '\\.(css|scss|jpg|png)$': '<rootDir>/empty-mock-module.js',
    },

Could somebody helps me whether I'm doing correct or not. I need to know how to map node_modules libraries in code. All the npm modules are working except my private module.

Solution

When the App is rendered in Jest it cannot find the 'root' element so one solution I have found is to provide a div element when the 'root' doesn't exist.

ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  document.getElementById('root') || document.createElement('div')
);

Answered By - Conor