adding a basic HMR test for tailwind styles

packages/astro/e2e/tailwindcss.test.js

@@ -1,5 +1,5 @@
 import { test as base, expect } from '@playwright/test';
-import { loadFixture } from './test-utils.js';
+import { loadFixture, onAfterHMR } from './test-utils.js';
 
 const test = base.extend({
 	astro: async ({}, use) => {
@@ -18,6 +18,10 @@ test.afterAll(async ({ astro }) => {
 	await devServer.stop();
 });
 
+test.afterEach(async ({ astro }) => {
+	astro.clean();
+});
+
 test('Tailwind CSS', async ({ page, astro }) => {
 	await page.goto(astro.resolveUrl('/'));
 
@@ -48,4 +52,23 @@ test('Tailwind CSS', async ({ page, astro }) => {
 		await expect(button, 'should have font-[900]').toHaveClass(/font-\[900\]/);
 		await expect(button, 'should have font weight').toHaveCSS('font-weight', '900');
 	});
+
+	await test.step('HMR', async () => {
+		const afterHMR = onAfterHMR(page);
+
+		await astro.writeFile(
+			'src/components/Button.astro',
+			(original) => original.replace('bg-purple-600', 'bg-purple-400')
+		);
+
+		await afterHMR;
+
+		const button = page.locator('button');
+		
+		await expect(button, 'should have bg-purple-400').toHaveClass(/bg-purple-400/);
+		await expect(button, 'should have background color').toHaveCSS(
+			'background-color',
+			'rgb(192, 132, 252)'
+		);
+	});
 });

packages/astro/e2e/test-utils.js

@@ -11,3 +11,7 @@ export function loadFixture(inlineConfig) {
 		root: new URL(inlineConfig.root, import.meta.url).toString()
 	})
 }
+
+export function onAfterHMR(page) {
+	return page.waitForEvent('console', message => message.text() === 'astro:hmr:after')
+}

packages/astro/src/runtime/client/hmr.ts

@@ -14,7 +14,11 @@ if (import.meta.hot) {
 				root.innerHTML = current?.innerHTML;
 			}
 		}
-		return diff(document, doc);
+		const result = diff(document, doc);
+
+		// event used for synchronizing E2E tests
+		console.log('astro:hmr:after');
+		return result;
 	}
 	async function updateAll(files: any[]) {
 		let hasAstroUpdate = false;
@@ -31,7 +35,7 @@ if (import.meta.hot) {
 			}
 		}
 		if (hasAstroUpdate) {
-			return updatePage();
+			return await updatePage();
 		}
 	}
 	import.meta.hot.on('vite:beforeUpdate', async (event) => {

packages/astro/test/test-utils.js

@@ -28,6 +28,7 @@ polyfill(globalThis, {
  * @property {(url: string) => string} resolveUrl
  * @property {(url: string, opts: any) => Promise<Response>} fetch
  * @property {(path: string) => Promise<string>} readFile
+ * @property {(path: string, updater: (content: string) => string) => Promise<void>} writeFile
  * @property {(path: string) => Promise<string[]>} readdir
  * @property {() => Promise<DevServer>} startDevServer
  * @property {() => Promise<PreviewServer>} preview
@@ -96,6 +97,17 @@ export async function loadFixture(inlineConfig) {
 
 	const resolveUrl = (url) => `http://${'127.0.0.1'}:${config.server.port}${url.replace(/^\/?/, '/')}`;
 
+	let cleanupCallbacks = [];
+
+	async function writeFile(filePath, updater) {
+		const pathname = new URL(filePath.replace(/^\//, ''), config.root);
+		const initial = await fs.promises.readFile(pathname, 'utf8');
+		
+		await fs.promises.writeFile(pathname, updater(initial), 'utf-8');
+
+		cleanupCallbacks.push(() => fs.promises.writeFile(pathname, initial, 'utf-8'));
+	}
+
 	return {
 		build: (opts = {}) => build(config, { mode: 'development', logging, telemetry, ...opts }),
 		startDevServer: async (opts = {}) => {
@@ -113,8 +125,12 @@ export async function loadFixture(inlineConfig) {
 		},
 		readFile: (filePath) =>
 			fs.promises.readFile(new URL(filePath.replace(/^\//, ''), config.outDir), 'utf8'),
+		writeFile,
 		readdir: (fp) => fs.promises.readdir(new URL(fp.replace(/^\//, ''), config.outDir)),
-		clean: () => fs.promises.rm(config.outDir, { maxRetries: 10, recursive: true, force: true }),
+		clean: async () => {
+			await fs.promises.rm(config.outDir, { maxRetries: 10, recursive: true, force: true });
+			await Promise.all(cleanupCallbacks.map(cb => cb()));
+		},
 		loadTestAdapterApp: async () => {
 			const url = new URL('./server/entry.mjs', config.outDir);
 			const { createApp } = await import(url);