Web components testing strategy

[ttalbot]

The goal of this issue is to define unit testing strategy for web components. All the following should be done for it to be considered complete:

• [x] Research unit tests frameworks for Web Components
• [x] Min 80% unit tests coverage for button
• [x] Min 80% unit tests coverage for card
• [x] Min 80% unit tests coverage for divider (?)
• [x] Min 80% unit tests coverage for logo (?)
• [x] Min 80% unit tests coverage for search-input
• [x] Update documentation
• [x] Allow unit tests to be ran only for 1 component
• [x] Add base test in WC generator

[bcldvd]

Playwright has been identified as a great candidate for testing web components, especially on his ability to pierce shadow DOM via simplified selectors: https://playwright.dev/docs/selectors/#selecting-elements-in-shadow-dom

Various inspirations:

• https://github.com/adobe/spectrum-web-components
• https://github.com/ing-bank/lion
• https://github.com/material-components/material-web
• https://github.com/modernweb-dev/web/tree/master/packages/test-runner-playwright
• https://lwc.dev/guide/test

[bcldvd]

This story will be left using only a global web-test-runner for all web-components, since all of them are at the moment written in LitElement.

Once we have some contributions with other frameworks, we'll make a separate test process that launches tests from the inner package of a given web component. Resulting lcov.info will be added to codecov in the files attribute of the wc-pr-build.yml This could be used as an starting point: https://github.com/code2nguyen/finastra-web-components/blob/testing-workflow/scripts/test.js