improve preview reliability - fix broken tests

.npmrc

@@ -3,8 +3,6 @@ prefer-workspace-packages=true
 link-workspace-packages=true
 save-workspace-protocol=false # This prevents the examples to have the `workspace:` prefix
 
-use-node-version=14.19.0
-
 # Rather than shamefully hoisting everything, just make problematic packages public
 public-hoist-pattern[]=autoprefixer
 public-hoist-pattern[]=astro

packages/astro/src/core/preview/index.ts

@@ -23,6 +23,8 @@ export interface PreviewServer {
 	stop(): Promise<void>;
 }
 
+const HAS_FILE_EXTENSION_REGEXP = /^.*\.[^\\]+$/;
+
 /** The primary dev action */
 export default async function preview(config: AstroConfig, { logging }: PreviewOptions): Promise<PreviewServer> {
 	const startServerTime = performance.now();
@@ -60,6 +62,9 @@ export default async function preview(config: AstroConfig, { logging }: PreviewO
 			case hasTrailingSlash && trailingSlash == 'never' && !isRoot:
 				sendError('Not Found (devOptions.trailingSlash is set to "never")');
 				return;
+			case !hasTrailingSlash && trailingSlash == 'always' && !isRoot && !HAS_FILE_EXTENSION_REGEXP.test(pathname):
+				sendError('Not Found (devOptions.trailingSlash is set to "always")');
+				return;
 			default: {
 				// HACK: rewrite req.url so that sirv finds the file
 				req.url = '/' + req.url?.replace(baseURL.pathname, '')

packages/astro/test/preview-routing.test.js

@@ -12,6 +12,9 @@ describe('Preview Routing', () => {
 			before(async () => {
 				fixture = await loadFixture({
 					projectRoot: './fixtures/with-subpath-no-trailing-slash/',
+					buildOptions: {
+						pageUrlFormat: 'directory',
+					},
 					devOptions: {
 						trailingSlash: 'never',
 						port: 4000,