First stab at adding support for running tests in a headless browser

[DmitrySharabin]

Uses Playwright under the hood. To keep hTest small, none of the browser binaries are installed by default.

One can run npx playwright install to install all the browsers, or npm install @playwright/browser-chromium, npm install @playwright/browser-firefox, npm install @playwright/browser-webkit to install Chromium, Firefox, or Webkit browser, respectively. We should probably add a note on this in our docs.

On the first run, if no browser binary is downloaded, Playwright will show a friendly message:

Down there is a small demo that shows all the tests we have successfully run in a headless browser. Console formatting tests are ignored since they (not dynamically) import the Chalk package, but the browser didn't choke on them. We should probably add a separate message about what tests were ignored and why.

In the video, you can see a (intentionally) falling test from these tests (not in the PR):

export default {
	name: "DOM tests",
	description: "Tests that are supposed to run in a browser",
	tests: [
		{
			run: () => Boolean(document.body),
			expect: true,
		},
		{
			name: "Document title is equal to “Foo”",
			run: () => document.title,
			expect: "Foo",
		},
	],
};

hTest.Run.in.Headless.Browser.mp4

[netlify]

✅ Deploy Preview for h-test ready!

Name	Link
🔨 Latest commit	57bc7eb
🔍 Latest deploy log	https://app.netlify.com/projects/h-test/deploys/693c904e6fb6780008b8fa1c
😎 Deploy Preview	https://deploy-preview-92--h-test.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.