simpleLWC.test.js

import { createElement } from 'lwc';
import HelloWorld from 'c/helloWorld';

describe('c-hello-world', () => {
    afterEach(() => {
        // The jsdom instance is shared across test cases in a single file so reset the DOM
        while (document.body.firstChild) {
            document.body.removeChild(document.body.firstChild);
        }
    });

    it('displays the correct message', () => {
        // Create element
        const element = createElement('c-hello-world', {
            is: HelloWorld
        });
        document.body.appendChild(element);

        // Get message from component
        const message = element.shadowRoot.querySelector('p');
        expect(message.textContent).toBe('Hello, World!');
    });
});