Add test to verify Lit works in SSR (withastro#3158)

test/fixtures/lit-element/src/components/my-element.js

@@ -24,11 +24,13 @@ export class MyElement extends LitElement {
     this.reflectedStr = 'default reflected string';
   }
   render() {
+		let typeofwindow = typeof window.Window;
     return html`
       <div>Testing...</div>
       <div id="bool">${this.bool ? 'A' : 'B'}</div>
       <div id="str">${this.str}</div>
       <div id="data">data: ${this.obj.data}</div>
+			<div id="win">${typeofwindow}</div>
     `;
   }
 }

test/ssr-lit.test.js

@@ -0,0 +1,34 @@
+import { expect } from 'chai';
+import { load as cheerioLoad } from 'cheerio';
+import { loadFixture } from './test-utils.js';
+import testAdapter from './test-adapter.js';
+
+describe('Lit integration in SSR', () => {
+	/** @type {import('./test-utils').Fixture} */
+	let fixture;
+
+	before(async () => {
+		fixture = await loadFixture({
+			root: './fixtures/lit-element/',
+			experimental: {
+				ssr: true,
+			},
+			adapter: testAdapter(),
+		});
+		await fixture.build();
+	});
+
+	async function fetchHTML(path) {
+		const app = await fixture.loadTestAdapterApp();
+		const request = new Request('http://example.com' + path);
+		const response = await app.render(request);
+		const html = await response.text();
+		return html;
+	}
+
+	it('Is able to load', async () => {
+		const html = await fetchHTML('/');
+		const $ = cheerioLoad(html);
+		expect($('#win').text()).to.equal('function');
+	});
+});