Fix AstroContainer usage in Vitest client environments (#14894)

Author: delucis

.changeset/icy-impalas-pay.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes support for Astro component rendering in Vitest test suites using a “client” environment such as `happy-dom` or `jsdom`

packages/astro/src/vite-plugin-astro/index.ts

@@ -231,7 +231,14 @@ export default function astro({ settings, logger }: AstroPluginOptions): vite.Pl
 
 			// If an Astro component is imported in code used on the client, we return an empty
 			// module so that Vite doesn’t bundle the server-side Astro code for the client.
-			if (!options?.ssr) {
+			if (
+				!options?.ssr &&
+				// Workaround to allow tests run with Vitest in a “client” environment to still render
+				// Astro components. See https://github.com/withastro/astro/issues/14883
+				// TODO: In a future major we should remove this and require people test Astro rendering in
+				// an SSR test environment, which more closely matches the real-world Vite environment.
+				!process.env.VITEST
+			) {
 				return {
 					code: `export default import.meta.env.DEV
 									? () => {