Skip dev server setup in configureServer when running inside Vitest (#17248)

* fix(server): skip dev server plugin setup in Vitest to prevent wrapDynamicImport crash (#16275)

* Apply suggestion from @matthewp

---------

Co-authored-by: Matthew Phillips <matthewphillips@cloudflare.com>

Author: astrobot-houston

.changeset/sweet-trains-follow.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes a crash when using Astro's `getViteConfig` with Vitest browser mode (e.g., Storybook vitest runner). Astro now skips dev server setup inside Vitest, preventing errors.

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

@@ -35,6 +35,14 @@ export default function createVitePluginAstroServer({
 			return environment.name === ASTRO_VITE_ENVIRONMENT_NAMES.ssr;
 		},
 		async configureServer(viteServer) {
+			// Skip Astro dev server setup when running inside Vitest. The dev server
+			// middleware (SSR handler, prerender handler, trailing-slash redirects, etc.)
+			// is only needed for `astro dev` and can crash in Vitest's browser server
+			// where the module evaluator may not support dynamic imports.
+			if (process.env.VITEST) {
+				return;
+			}
+
 			const ssrEnvironment = viteServer.environments[ASTRO_VITE_ENVIRONMENT_NAMES.ssr];
 			const prerenderEnvironment = viteServer.environments[ASTRO_VITE_ENVIRONMENT_NAMES.prerender];
 

packages/astro/test/units/vite-plugin-astro-server/vitest-guard.test.ts

@@ -0,0 +1,46 @@
+import assert from 'node:assert/strict';
+import { afterEach, describe, it } from 'node:test';
+import createVitePluginAstroServer from '../../../dist/vite-plugin-astro-server/plugin.js';
+import { createBasicSettings } from '../test-utils.ts';
+import { defaultLogger } from '../test-utils.ts';
+
+describe('astro:server configureServer vitest guard', () => {
+	const originalVitest = process.env.VITEST;
+
+	afterEach(() => {
+		if (originalVitest !== undefined) {
+			process.env.VITEST = originalVitest;
+		} else {
+			delete process.env.VITEST;
+		}
+	});
+
+	it('skips server setup when process.env.VITEST is set', async () => {
+		process.env.VITEST = 'true';
+		const settings = await createBasicSettings({});
+		const plugin = createVitePluginAstroServer({ settings, logger: defaultLogger });
+
+		// configureServer should return early without throwing when VITEST is set,
+		// even with a fake viteServer that has no environments
+		const fakeViteServer = {} as any;
+		const result = await (plugin as any).configureServer(fakeViteServer);
+
+		// Early return produces undefined (no middleware callback)
+		assert.equal(result, undefined);
+	});
+
+	it('attempts server setup when process.env.VITEST is not set', async () => {
+		delete process.env.VITEST;
+		const settings = await createBasicSettings({});
+		const plugin = createVitePluginAstroServer({ settings, logger: defaultLogger });
+
+		// Without VITEST, configureServer should try to access viteServer.environments
+		// and fail because our fake server has none
+		const fakeViteServer = { environments: {} } as any;
+		// Should not throw — it will just have no runnable environments
+		const result = await (plugin as any).configureServer(fakeViteServer);
+
+		// When there are no runnable environments, it returns a middleware setup function
+		assert.equal(typeof result, 'function');
+	});
+});