If you choose the testing option in the project generator it will scaffold some example tests for your component.
We recommend @web/test-runner for testing web components. It's based on
@web/dev-server, following the same approach using native es modules, and runs tests in a real browser.
To run the tests, execute this command:
npm run test
This will run the tests in a locally installed Chrome browser. There are many other browser options in Web Test Runner as well.
To run the tests in watch mode, execute this command:
npm run test:watch
This will keep the test runner open. Editing files will re-run the associated tests.
Follow this guide for a full step by step guide on using Web Test Runner