diff --git a/packages/astro/test/units/app/dev-url-construction.test.js b/packages/astro/test/units/app/dev-url-construction.test.ts
similarity index 92%
rename from packages/astro/test/units/app/dev-url-construction.test.js
rename to packages/astro/test/units/app/dev-url-construction.test.ts
index c273991369c8..ab752b98e2ce 100644
--- a/packages/astro/test/units/app/dev-url-construction.test.js
+++ b/packages/astro/test/units/app/dev-url-construction.test.ts
@@ -1,22 +1,22 @@
 import * as assert from 'node:assert/strict';
 import { describe, it } from 'node:test';
+import type { SSRManifest } from '../../../dist/core/app/types.js';
 import {
 	getFirstForwardedValue,
 	validateForwardedHeaders,
 } from '../../../dist/core/app/validate-headers.js';
 
-/**
- * Mirrors the URL construction logic in AstroServerApp.handleRequest so that
- * the protocol and host derivation can be exercised in isolation.
- *
- * @param {object} opts
- * @param {Record<string, string>} opts.headers - Incoming request headers
- * @param {boolean} [opts.isHttps=false] - Whether Vite itself is running TLS
- * @param {import('../../../dist/core/app/types.js').SSRManifest['allowedDomains']} [opts.allowedDomains]
- * @param {string} [opts.requestUrl='/']
- * @returns {URL}
- */
-function buildDevUrl({ headers, isHttps = false, allowedDomains, requestUrl = '/' }) {
+function buildDevUrl({
+	headers,
+	isHttps = false,
+	allowedDomains,
+	requestUrl = '/',
+}: {
+	headers: Record<string, string>;
+	isHttps?: boolean;
+	allowedDomains?: SSRManifest['allowedDomains'];
+	requestUrl?: string;
+}): URL {
 	const validated = validateForwardedHeaders(
 		getFirstForwardedValue(headers['x-forwarded-proto']),
 		getFirstForwardedValue(headers['x-forwarded-host']),
diff --git a/packages/astro/test/units/app/headers.test.js b/packages/astro/test/units/app/headers.test.ts
similarity index 100%
rename from packages/astro/test/units/app/headers.test.js
rename to packages/astro/test/units/app/headers.test.ts
diff --git a/packages/astro/test/units/app/url-attribute-xss.test.js b/packages/astro/test/units/app/url-attribute-xss.test.ts
similarity index 98%
rename from packages/astro/test/units/app/url-attribute-xss.test.js
rename to packages/astro/test/units/app/url-attribute-xss.test.ts
index 56aa4d401c90..3afd18d4a1f3 100644
--- a/packages/astro/test/units/app/url-attribute-xss.test.js
+++ b/packages/astro/test/units/app/url-attribute-xss.test.ts
@@ -1,4 +1,3 @@
-// @ts-check
 import assert from 'node:assert/strict';
 import { describe, it } from 'node:test';
 import { addAttribute } from '../../../dist/runtime/server/render/util.js';
diff --git a/packages/astro/test/units/assets/image-layout.test.js b/packages/astro/test/units/assets/image-layout.test.ts
similarity index 100%
rename from packages/astro/test/units/assets/image-layout.test.js
rename to packages/astro/test/units/assets/image-layout.test.ts
diff --git a/packages/astro/test/units/render/escape.test.js b/packages/astro/test/units/render/escape.test.ts
similarity index 90%
rename from packages/astro/test/units/render/escape.test.js
rename to packages/astro/test/units/render/escape.test.ts
index e38af171cc18..19e8402a01ac 100644
--- a/packages/astro/test/units/render/escape.test.js
+++ b/packages/astro/test/units/render/escape.test.ts
@@ -1,4 +1,3 @@
-// @ts-check
 import assert from 'node:assert/strict';
 import { describe, it } from 'node:test';
 import {
@@ -86,8 +85,8 @@ describe('unescapeHTML', () => {
 			yield '<li>1</li>';
 			yield '<li>2</li>';
 		}
-		const result = unescapeHTML(gen());
-		const chunks = [];
+		const result = unescapeHTML(gen()) as AsyncIterable<unknown>;
+		const chunks: string[] = [];
 		for await (const chunk of result) {
 			chunks.push(String(chunk));
 		}
@@ -100,8 +99,8 @@ describe('unescapeHTML', () => {
 			yield '<li>a</li>';
 			yield '<li>b</li>';
 		}
-		const result = unescapeHTML(gen());
-		const chunks = [];
+		const result = unescapeHTML(gen()) as AsyncIterable<unknown>;
+		const chunks: string[] = [];
 		for await (const chunk of result) {
 			chunks.push(String(chunk));
 		}
@@ -110,8 +109,8 @@ describe('unescapeHTML', () => {
 
 	it('can take a Response', async () => {
 		const response = new Response('<p>hello</p>', { headers: { 'content-type': 'text/html' } });
-		const result = unescapeHTML(response);
-		const chunks = [];
+		const result = unescapeHTML(response) as AsyncIterable<unknown>;
+		const chunks: string[] = [];
 		const dec = new TextDecoder();
 		for await (const chunk of result) {
 			chunks.push(chunk instanceof Uint8Array ? dec.decode(chunk) : String(chunk));
@@ -126,8 +125,8 @@ describe('unescapeHTML', () => {
 				controller.close();
 			},
 		});
-		const result = unescapeHTML(stream);
-		const chunks = [];
+		const result = unescapeHTML(stream) as AsyncIterable<unknown>;
+		const chunks: string[] = [];
 		for await (const chunk of result) {
 			chunks.push(String(chunk));
 		}
diff --git a/packages/astro/test/units/render/hydration.test.js b/packages/astro/test/units/render/hydration.test.ts
similarity index 96%
rename from packages/astro/test/units/render/hydration.test.js
rename to packages/astro/test/units/render/hydration.test.ts
index 5b11e90a9564..afc22e94978d 100644
--- a/packages/astro/test/units/render/hydration.test.js
+++ b/packages/astro/test/units/render/hydration.test.ts
@@ -1,4 +1,3 @@
-// @ts-check
 import assert from 'node:assert/strict';
 import { describe, it } from 'node:test';
 import { extractDirectives } from '../../../dist/runtime/server/hydration.js';
@@ -138,9 +137,9 @@ describe('extractDirectives', () => {
 	it('throws for an invalid hydration directive', () => {
 		assert.throws(
 			() => extractDirectives({ 'client:unknown': '' }, clientDirectives),
-			(err) => {
-				assert.ok(err.message.includes('invalid hydration directive'));
-				assert.ok(err.message.includes('client:unknown'));
+			(err: unknown) => {
+				assert.ok((err as Error).message.includes('invalid hydration directive'));
+				assert.ok((err as Error).message.includes('client:unknown'));
 				return true;
 			},
 		);
diff --git a/packages/astro/test/units/routing/origin-pathname.test.js b/packages/astro/test/units/routing/origin-pathname.test.ts
similarity index 100%
rename from packages/astro/test/units/routing/origin-pathname.test.js
rename to packages/astro/test/units/routing/origin-pathname.test.ts
diff --git a/packages/astro/test/units/routing/routing-helpers.test.js b/packages/astro/test/units/routing/routing-helpers.test.ts
similarity index 65%
rename from packages/astro/test/units/routing/routing-helpers.test.js
rename to packages/astro/test/units/routing/routing-helpers.test.ts
index 8f01ae7abf4e..305db1ecbbb1 100644
--- a/packages/astro/test/units/routing/routing-helpers.test.js
+++ b/packages/astro/test/units/routing/routing-helpers.test.ts
@@ -1,27 +1,31 @@
-// @ts-check
 import assert from 'node:assert/strict';
 import { describe, it } from 'node:test';
+import type { RouteData } from '../../../dist/types/public/internal.js';
 import { hasNonPrerenderedRoute } from '../../../dist/core/routing/helpers.js';
 
+function route(overrides: Partial<RouteData>): RouteData {
+	return overrides as RouteData;
+}
+
 describe('hasNonPrerenderedRoute', () => {
 	it('returns true when a non-prerendered project page exists', () => {
-		const routes = [{ type: 'page', origin: 'project', prerender: false }];
+		const routes = [route({ type: 'page', origin: 'project', prerender: false })];
 		assert.equal(hasNonPrerenderedRoute(routes), true);
 	});
 
 	it('returns false when all project pages are prerendered', () => {
-		const routes = [{ type: 'page', origin: 'project', prerender: true }];
+		const routes = [route({ type: 'page', origin: 'project', prerender: true })];
 		assert.equal(hasNonPrerenderedRoute(routes), false);
 	});
 
 	it('excludes endpoints when includeEndpoints is false', () => {
-		const routes = [{ type: 'endpoint', origin: 'project', prerender: false }];
+		const routes = [route({ type: 'endpoint', origin: 'project', prerender: false })];
 		assert.equal(hasNonPrerenderedRoute(routes, { includeEndpoints: false }), false);
 		assert.equal(hasNonPrerenderedRoute(routes, { includeEndpoints: true }), true);
 	});
 
 	it('returns true for injected (external) non-prerendered pages when includeExternal is true', () => {
-		const routes = [{ type: 'page', origin: 'external', prerender: false }];
+		const routes = [route({ type: 'page', origin: 'external', prerender: false })];
 		assert.equal(hasNonPrerenderedRoute(routes, { includeExternal: true }), true);
 		assert.equal(hasNonPrerenderedRoute(routes), false);
 	});