diff --git a/packages/integrations/netlify/package.json b/packages/integrations/netlify/package.json
index 5cbe0a5c6bbd..a8b9bca7ab39 100644
--- a/packages/integrations/netlify/package.json
+++ b/packages/integrations/netlify/package.json
@@ -33,10 +33,11 @@
     "build": "astro-scripts build \"src/**/*.ts\" && tsc",
     "build:ci": "astro-scripts build \"src/**/*.ts\"",
     "test": "pnpm run test-fn && pnpm run test-static && pnpm run test:dev",
-    "test-fn": "astro-scripts test \"test/functions/*.test.js\"",
-    "test:dev": "astro-scripts test \"test/development/*.test.js\"",
-    "test-static": "astro-scripts test \"test/static/*.test.js\"",
-    "test:hosted": "astro-scripts test \"test/hosted/*.test.js\""
+    "test-fn": "astro-scripts test \"test/functions/*.test.ts\"",
+    "test:dev": "astro-scripts test \"test/development/*.test.ts\"",
+    "test-static": "astro-scripts test \"test/static/*.test.ts\"",
+    "test:hosted": "astro-scripts test \"test/hosted/*.test.js\"",
+    "typecheck:tests": "tsc --build tsconfig.test.json"
   },
   "dependencies": {
     "@astrojs/internal-helpers": "workspace:*",
diff --git a/packages/integrations/netlify/test/development/primitives.test.js b/packages/integrations/netlify/test/development/primitives.test.ts
similarity index 88%
rename from packages/integrations/netlify/test/development/primitives.test.js
rename to packages/integrations/netlify/test/development/primitives.test.ts
index 016305e42cae..a8fa8ae4db67 100644
--- a/packages/integrations/netlify/test/development/primitives.test.js
+++ b/packages/integrations/netlify/test/development/primitives.test.ts
@@ -2,14 +2,13 @@ import assert from 'node:assert/strict';
 import { after, afterEach, before, describe, it } from 'node:test';
 
 import * as cheerio from 'cheerio';
-import { loadFixture } from '../../../../astro/test/test-utils.js';
+import { type DevServer, type Fixture, loadFixture } from '../../../../astro/test/test-utils.js';
 import netlifyAdapter from '../../dist/index.js';
 
 describe('Netlify primitives', () => {
 	describe('Development', () => {
-		/** @type {import('../../../../astro/test/test-utils').Fixture} */
-		let fixture;
-		let devServer;
+		let fixture: Fixture;
+		let devServer: DevServer;
 		before(async () => {
 			fixture = await loadFixture({
 				root: new URL('./fixtures/primitives/', import.meta.url),
@@ -65,9 +64,11 @@ describe('Netlify primitives', () => {
 		it('loads images in development', async () => {
 			const imgResponse = await fixture.fetch('/astronaut');
 			const $img = cheerio.load(await imgResponse.text());
-			const images = $img('img').map((_i, el) => {
-				return $img(el).attr('src');
-			});
+			const images = $img('img')
+				.map((_i, el) => {
+					return $img(el).attr('src');
+				})
+				.toArray();
 
 			for (const imgSrc of images) {
 				assert(imgSrc.startsWith('/.netlify/images'));
@@ -89,9 +90,11 @@ describe('Netlify primitives', () => {
 			try {
 				const imgResponse = await cdnDisabledFixture.fetch('/astronaut');
 				const $img = cheerio.load(await imgResponse.text());
-				const images = $img('img').map((_i, el) => {
-					return $img(el).attr('src');
-				});
+				const images = $img('img')
+					.map((_i, el) => {
+						return $img(el).attr('src');
+					})
+					.toArray();
 
 				for (const imgSrc of images) {
 					assert(
@@ -101,7 +104,7 @@ describe('Netlify primitives', () => {
 				}
 			} finally {
 				await cdnDisabledServer.stop();
-				process.env.DISABLE_IMAGE_CDN = undefined;
+				delete process.env.DISABLE_IMAGE_CDN;
 			}
 		});
 	});
diff --git a/packages/integrations/netlify/test/functions/cookies.test.js b/packages/integrations/netlify/test/functions/cookies.test.js
deleted file mode 100644
index 6ef16763ed5d..000000000000
--- a/packages/integrations/netlify/test/functions/cookies.test.js
+++ /dev/null
@@ -1,65 +0,0 @@
-import * as assert from 'node:assert/strict';
-import { before, describe, it } from 'node:test';
-import { loadFixture } from '../../../../astro/test/test-utils.js';
-
-describe(
-	'Cookies',
-	() => {
-		let fixture;
-
-		before(async () => {
-			fixture = await loadFixture({ root: new URL('./fixtures/cookies/', import.meta.url) });
-			await fixture.build();
-		});
-
-		it('Can set multiple', async () => {
-			const entryURL = new URL(
-				'./fixtures/cookies/.netlify/v1/functions/ssr/ssr.mjs',
-				import.meta.url,
-			);
-			const { default: handler } = await import(entryURL);
-			const resp = await handler(
-				new Request('http://example.com/login', { method: 'POST', body: '{}' }),
-				{},
-			);
-			assert.equal(resp.status, 301);
-			assert.equal(resp.headers.get('location'), '/');
-			assert.deepEqual(resp.headers.getSetCookie(), ['foo=foo; HttpOnly', 'bar=bar; HttpOnly']);
-		});
-
-		it('Can set partitioned cookie', async () => {
-			const entryURL = new URL(
-				'./fixtures/cookies/.netlify/v1/functions/ssr/ssr.mjs',
-				import.meta.url,
-			);
-			const { default: handler } = await import(entryURL);
-			const resp = await handler(new Request('http://example.com/partitioned'), {});
-			assert.equal(resp.status, 200);
-			const cookie = resp.headers.getSetCookie()[0];
-			assert.ok(cookie.includes('Partitioned'), 'Cookie should include Partitioned attribute');
-		});
-
-		it('renders dynamic 404 page', async () => {
-			const entryURL = new URL(
-				'./fixtures/cookies/.netlify/v1/functions/ssr/ssr.mjs',
-				import.meta.url,
-			);
-			const { default: handler } = await import(entryURL);
-			const resp = await handler(
-				new Request('http://example.com/nonexistant-page', {
-					headers: {
-						'x-test': 'bar',
-					},
-				}),
-				{},
-			);
-			assert.equal(resp.status, 404);
-			const text = await resp.text();
-			assert.equal(text.includes('This is my custom 404 page'), true);
-			assert.equal(text.includes('x-test: bar'), true);
-		});
-	},
-	{
-		timeout: 120000,
-	},
-);
diff --git a/packages/integrations/netlify/test/functions/cookies.test.ts b/packages/integrations/netlify/test/functions/cookies.test.ts
new file mode 100644
index 000000000000..d3c0f7d434db
--- /dev/null
+++ b/packages/integrations/netlify/test/functions/cookies.test.ts
@@ -0,0 +1,59 @@
+import * as assert from 'node:assert/strict';
+import { before, describe, it } from 'node:test';
+import { type Fixture, loadFixture } from '../../../../astro/test/test-utils.js';
+
+describe('Cookies', { timeout: 120000 }, () => {
+	let fixture: Fixture;
+
+	before(async () => {
+		fixture = await loadFixture({ root: new URL('./fixtures/cookies/', import.meta.url) });
+		await fixture.build({});
+	});
+
+	it('Can set multiple', async () => {
+		const entryURL = new URL(
+			'./fixtures/cookies/.netlify/v1/functions/ssr/ssr.mjs',
+			import.meta.url,
+		);
+		const { default: handler } = await import(entryURL.href);
+		const resp = await handler(
+			new Request('http://example.com/login', { method: 'POST', body: '{}' }),
+			{},
+		);
+		assert.equal(resp.status, 301);
+		assert.equal(resp.headers.get('location'), '/');
+		assert.deepEqual(resp.headers.getSetCookie(), ['foo=foo; HttpOnly', 'bar=bar; HttpOnly']);
+	});
+
+	it('Can set partitioned cookie', async () => {
+		const entryURL = new URL(
+			'./fixtures/cookies/.netlify/v1/functions/ssr/ssr.mjs',
+			import.meta.url,
+		);
+		const { default: handler } = await import(entryURL.href);
+		const resp = await handler(new Request('http://example.com/partitioned'), {});
+		assert.equal(resp.status, 200);
+		const cookie = resp.headers.getSetCookie()[0];
+		assert.ok(cookie.includes('Partitioned'), 'Cookie should include Partitioned attribute');
+	});
+
+	it('renders dynamic 404 page', async () => {
+		const entryURL = new URL(
+			'./fixtures/cookies/.netlify/v1/functions/ssr/ssr.mjs',
+			import.meta.url,
+		);
+		const { default: handler } = await import(entryURL.href);
+		const resp = await handler(
+			new Request('http://example.com/nonexistant-page', {
+				headers: {
+					'x-test': 'bar',
+				},
+			}),
+			{},
+		);
+		assert.equal(resp.status, 404);
+		const text = await resp.text();
+		assert.equal(text.includes('This is my custom 404 page'), true);
+		assert.equal(text.includes('x-test: bar'), true);
+	});
+});
diff --git a/packages/integrations/netlify/test/functions/edge-middleware.test.js b/packages/integrations/netlify/test/functions/edge-middleware.test.js
deleted file mode 100644
index 6d255f4dc7f9..000000000000
--- a/packages/integrations/netlify/test/functions/edge-middleware.test.js
+++ /dev/null
@@ -1,66 +0,0 @@
-import * as assert from 'node:assert/strict';
-import { after, before, describe, it } from 'node:test';
-import { loadFixture } from '../../../../astro/test/test-utils.js';
-
-describe(
-	'Middleware',
-	() => {
-		const root = new URL('./fixtures/middleware/', import.meta.url);
-
-		describe('middlewareMode: classic', () => {
-			let fixture;
-			before(async () => {
-				process.env.EDGE_MIDDLEWARE = 'false';
-				fixture = await loadFixture({ root });
-				await fixture.build();
-			});
-
-			it('emits no edge function', async () => {
-				assert.equal(
-					fixture.pathExists('../.netlify/v1/edge-functions/middleware/middleware.mjs'),
-					false,
-				);
-			});
-
-			it('applies middleware to static files at build-time', async () => {
-				// prerendered page has middleware applied at build time
-				const prerenderedPage = await fixture.readFile('prerender/index.html');
-				assert.equal(prerenderedPage.includes('<title>Middleware</title>'), true);
-			});
-
-			after(async () => {
-				process.env.EDGE_MIDDLEWARE = undefined;
-				await fixture.clean();
-			});
-		});
-
-		describe('middlewareMode: edge', () => {
-			let fixture;
-			before(async () => {
-				process.env.EDGE_MIDDLEWARE = 'true';
-				fixture = await loadFixture({ root });
-				await fixture.build();
-			});
-
-			it('emits an edge function', async () => {
-				const contents = await fixture.readFile(
-					'../.netlify/v1/edge-functions/middleware/middleware.mjs',
-				);
-				assert.equal(contents.includes('"Hello world"'), false);
-			});
-
-			it.skip('does not apply middleware during prerendering', async () => {
-				const prerenderedPage = await fixture.readFile('prerender/index.html');
-				assert.equal(prerenderedPage.includes('<title></title>'), true);
-			});
-
-			after(async () => {
-				process.env.EDGE_MIDDLEWARE = undefined;
-				await fixture.clean();
-			});
-		});
-	},
-	{
-		timeout: 120000,
-	},
-);
diff --git a/packages/integrations/netlify/test/functions/edge-middleware.test.ts b/packages/integrations/netlify/test/functions/edge-middleware.test.ts
new file mode 100644
index 000000000000..e1a667c83924
--- /dev/null
+++ b/packages/integrations/netlify/test/functions/edge-middleware.test.ts
@@ -0,0 +1,60 @@
+import * as assert from 'node:assert/strict';
+import { after, before, describe, it } from 'node:test';
+import { type Fixture, loadFixture } from '../../../../astro/test/test-utils.js';
+
+describe('Middleware', { timeout: 120000 }, () => {
+	const root = new URL('./fixtures/middleware/', import.meta.url);
+
+	describe('middlewareMode: classic', () => {
+		let fixture: Fixture;
+		before(async () => {
+			process.env.EDGE_MIDDLEWARE = 'false';
+			fixture = await loadFixture({ root });
+			await fixture.build({});
+		});
+
+		it('emits no edge function', async () => {
+			assert.equal(
+				fixture.pathExists('../.netlify/v1/edge-functions/middleware/middleware.mjs'),
+				false,
+			);
+		});
+
+		it('applies middleware to static files at build-time', async () => {
+			// prerendered page has middleware applied at build time
+			const prerenderedPage = await fixture.readFile('prerender/index.html');
+			assert.equal(prerenderedPage.includes('<title>Middleware</title>'), true);
+		});
+
+		after(async () => {
+			delete process.env.EDGE_MIDDLEWARE;
+			await fixture.clean();
+		});
+	});
+
+	describe('middlewareMode: edge', () => {
+		let fixture: Fixture;
+		before(async () => {
+			process.env.EDGE_MIDDLEWARE = 'true';
+			fixture = await loadFixture({ root });
+			await fixture.build({});
+		});
+
+		it('emits an edge function', async () => {
+			const contents = await fixture.readFile(
+				'../.netlify/v1/edge-functions/middleware/middleware.mjs',
+			);
+			assert.equal(contents.includes('"Hello world"'), false);
+		});
+
+		it.skip('does not apply middleware during prerendering', async () => {
+			const prerenderedPage = await fixture.readFile('prerender/index.html');
+			assert.equal(prerenderedPage.includes('<title></title>'), true);
+		});
+
+		after(async () => {
+			delete process.env.EDGE_MIDDLEWARE;
+			await fixture.clean();
+		});
+	});
+});
diff --git a/packages/integrations/netlify/test/functions/image-cdn.test.js b/packages/integrations/netlify/test/functions/image-cdn.test.js
deleted file mode 100644
index 8d6196817607..000000000000
--- a/packages/integrations/netlify/test/functions/image-cdn.test.js
+++ /dev/null
@@ -1,182 +0,0 @@
-import * as assert from 'node:assert/strict';
-import { after, before, describe, it } from 'node:test';
-import { remotePatternToRegex } from '@astrojs/netlify';
-import { loadFixture } from '../../../../astro/test/test-utils.js';
-import imageService from '../../dist/image-service.js';
-
-describe(
-	'Image CDN',
-	() => {
-		const root = new URL('./fixtures/middleware/', import.meta.url);
-
-		describe('configuration', () => {
-			after(() => {
-				process.env.DISABLE_IMAGE_CDN = undefined;
-			});
-
-			it('enables Netlify Image CDN', async () => {
-				const fixture = await loadFixture({ root });
-				await fixture.build();
-
-				const astronautPage = await fixture.readFile('astronaut/index.html');
-				assert.equal(astronautPage.includes(`src="/.netlify/image`), true);
-			});
-
-			it('respects image CDN opt-out', async () => {
-				process.env.DISABLE_IMAGE_CDN = 'true';
-				const fixture = await loadFixture({ root });
-				await fixture.build();
-
-				const astronautPage = await fixture.readFile('astronaut/index.html');
-				assert.equal(astronautPage.includes(`src="/_astro/astronaut.`), true);
-			});
-		});
-
-		describe('remote image config', () => {
-			let regexes;
-
-			before(async () => {
-				const fixture = await loadFixture({ root });
-				await fixture.build();
-
-				const config = await fixture.readFile('../.netlify/v1/config.json');
-				if (config) {
-					regexes = JSON.parse(config).images.remote_images.map((pattern) => new RegExp(pattern));
-				}
-			});
-
-			it('generates remote image config patterns', async () => {
-				assert.equal(regexes?.length, 3);
-			});
-
-			it('generates correct config for domains', async () => {
-				const domain = regexes[0];
-				assert.equal(domain.test('https://example.net/image.jpg'), true);
-				assert.equal(
-					domain.test('https://www.example.net/image.jpg'),
-					false,
-					'subdomain should not match',
-				);
-				assert.equal(domain.test('http://example.net/image.jpg'), true, 'http should match');
-				assert.equal(
-					domain.test('https://example.net/subdomain/image.jpg'),
-					true,
-					'subpath should match',
-				);
-				const subdomain = regexes[1];
-				assert.equal(
-					subdomain.test('https://secret.example.edu/image.jpg'),
-					true,
-					'should match subdomains',
-				);
-				assert.equal(
-					subdomain.test('https://secretxexample.edu/image.jpg'),
-					false,
-					'should not use dots in domains as wildcards',
-				);
-			});
-
-			it('generates correct config for remotePatterns', async () => {
-				const patterns = regexes[2];
-				assert.equal(
-					patterns.test('https://example.org/images/1.jpg'),
-					true,
-					'should match domain',
-				);
-				assert.equal(
-					patterns.test('https://www.example.org/images/2.jpg'),
-					true,
-					'www subdomain should match',
-				);
-				assert.equal(
-					patterns.test('https://www.subdomain.example.org/images/2.jpg'),
-					false,
-					'second level subdomain should not match',
-				);
-				assert.equal(
-					patterns.test('https://example.org/not-images/2.jpg'),
-					false,
-					'wrong path should not match',
-				);
-			});
-
-			it('warns when remotepatterns generates an invalid regex', async (t) => {
-				const logger = {
-					warn: t.mock.fn(),
-				};
-				const regex = remotePatternToRegex(
-					{
-						hostname: '*.examp[le.org',
-						pathname: '/images/*',
-					},
-					logger,
-				);
-				assert.strictEqual(regex, undefined);
-				const calls = logger.warn.mock.calls;
-				assert.strictEqual(calls.length, 1);
-				assert.equal(
-					calls[0].arguments[0],
-					'Could not generate a valid regex from the remotePattern "{"hostname":"*.examp[le.org","pathname":"/images/*"}". Please check the syntax.',
-				);
-			});
-		});
-
-		describe('fit parameter', () => {
-			it('includes fit parameter in image URL', () => {
-				const url = imageService.getURL({
-					src: 'images/astronaut.jpg',
-					width: 300,
-					height: 400,
-					fit: 'cover',
-					format: 'webp',
-				});
-				assert.ok(url.includes('fit=cover'), `Expected fit=cover in URL, got: ${url}`);
-			});
-
-			it('maps Astro fit values to Netlify equivalents', () => {
-				const cases = [
-					['contain', 'contain'],
-					['cover', 'cover'],
-					['fill', 'fill'],
-					['inside', 'contain'],
-					['outside', 'cover'],
-					['scale-down', 'contain'],
-				];
-				for (const [astroFit, netlifyFit] of cases) {
-					const url = imageService.getURL({
-						src: 'img.jpg',
-						width: 100,
-						height: 100,
-						fit: astroFit,
-					});
-					assert.ok(
-						url.includes(`fit=${netlifyFit}`),
-						`Expected fit=${netlifyFit} for astro fit="${astroFit}", got: ${url}`,
-					);
-				}
-			});
-
-			it('omits fit parameter when fit is none or unset', () => {
-				const withNone = imageService.getURL({
-					src: 'img.jpg',
-					width: 100,
-					height: 100,
-					fit: 'none',
-				});
-				assert.ok(
-					!withNone.includes('fit='),
-					`Expected no fit param for fit="none", got: ${withNone}`,
-				);
-
-				const withoutFit = imageService.getURL({ src: 'img.jpg', width: 100, height: 100 });
-				assert.ok(
-					!withoutFit.includes('fit='),
-					`Expected no fit param when unset, got: ${withoutFit}`,
-				);
-			});
-		});
-	},
-	{
-		timeout: 120000,
-	},
-);
diff --git a/packages/integrations/netlify/test/functions/image-cdn.test.ts b/packages/integrations/netlify/test/functions/image-cdn.test.ts
new file mode 100644
index 000000000000..4b8ed3783568
--- /dev/null
+++ b/packages/integrations/netlify/test/functions/image-cdn.test.ts
@@ -0,0 +1,179 @@
+import * as assert from 'node:assert/strict';
+import { after, before, describe, it } from 'node:test';
+import type { AstroIntegrationLogger } from 'astro';
+import { remotePatternToRegex } from '@astrojs/netlify';
+import { loadFixture } from '../../../../astro/test/test-utils.js';
+import imageService from '../../dist/image-service.js';
+
+describe('Image CDN', { timeout: 120000 }, () => {
+	const root = new URL('./fixtures/middleware/', import.meta.url);
+
+	describe('configuration', () => {
+		after(() => {
+			delete process.env.DISABLE_IMAGE_CDN;
+		});
+
+		it('enables Netlify Image CDN', async () => {
+			const fixture = await loadFixture({ root });
+			await fixture.build({});
+
+			const astronautPage = await fixture.readFile('astronaut/index.html');
+			assert.equal(astronautPage.includes(`src="/.netlify/image`), true);
+		});
+
+		it('respects image CDN opt-out', async () => {
+			process.env.DISABLE_IMAGE_CDN = 'true';
+			const fixture = await loadFixture({ root });
+			await fixture.build({});
+
+			const astronautPage = await fixture.readFile('astronaut/index.html');
+			assert.equal(astronautPage.includes(`src="/_astro/astronaut.`), true);
+		});
+	});
+
+	describe('remote image config', () => {
+		let regexes: RegExp[] | undefined;
+
+		before(async () => {
+			const fixture = await loadFixture({ root });
+			await fixture.build({});
+
+			const config = await fixture.readFile('../.netlify/v1/config.json');
+			if (config) {
+				regexes = JSON.parse(config).images.remote_images.map(
+					(pattern: string) => new RegExp(pattern),
+				);
+			}
+		});
+
+		it('generates remote image config patterns', async () => {
+			assert.equal(regexes?.length, 3);
+		});
+
+		it('generates correct config for domains', async () => {
+			const domain = regexes![0];
+			assert.equal(domain.test('https://example.net/image.jpg'), true);
+			assert.equal(
+				domain.test('https://www.example.net/image.jpg'),
+				false,
+				'subdomain should not match',
+			);
+			assert.equal(domain.test('http://example.net/image.jpg'), true, 'http should match');
+			assert.equal(
+				domain.test('https://example.net/subdomain/image.jpg'),
+				true,
+				'subpath should match',
+			);
+			const subdomain = regexes![1];
+			assert.equal(
+				subdomain.test('https://secret.example.edu/image.jpg'),
+				true,
+				'should match subdomains',
+			);
+			assert.equal(
+				subdomain.test('https://secretxexample.edu/image.jpg'),
+				false,
+				'should not use dots in domains as wildcards',
+			);
+		});
+
+		it('generates correct config for remotePatterns', async () => {
+			const patterns = regexes![2];
+			assert.equal(patterns.test('https://example.org/images/1.jpg'), true, 'should match domain');
+			assert.equal(
+				patterns.test('https://www.example.org/images/2.jpg'),
+				true,
+				'www subdomain should match',
+			);
+			assert.equal(
+				patterns.test('https://www.subdomain.example.org/images/2.jpg'),
+				false,
+				'second level subdomain should not match',
+			);
+			assert.equal(
+				patterns.test('https://example.org/not-images/2.jpg'),
+				false,
+				'wrong path should not match',
+			);
+		});
+
+		it('warns when remotepatterns generates an invalid regex', async (t) => {
+			const warnFn = t.mock.fn();
+			const logger = { warn: warnFn } as unknown as AstroIntegrationLogger;
+			const regex = remotePatternToRegex(
+				{
+					hostname: '*.examp[le.org',
+					pathname: '/images/*',
+				},
+				logger,
+			);
+			assert.strictEqual(regex, undefined);
+			const calls = warnFn.mock.calls;
+			assert.strictEqual(calls.length, 1);
+			assert.equal(
+				calls[0].arguments[0],
+				'Could not generate a valid regex from the remotePattern "{"hostname":"*.examp[le.org","pathname":"/images/*"}". Please check the syntax.',
+			);
+		});
+	});
+
+	describe('fit parameter', () => {
+		// imageService.getURL is typed as returning string | Promise<string>, but this
+		// implementation always returns a string synchronously
+		// eslint-disable-next-line @typescript-eslint/no-explicit-any
+		const getURL = (options: any): string => imageService.getURL(options, {} as any) as string;
+
+		it('includes fit parameter in image URL', () => {
+			const url = getURL({
+				src: 'images/astronaut.jpg',
+				width: 300,
+				height: 400,
+				fit: 'cover',
+				format: 'webp',
+			});
+			assert.ok(url.includes('fit=cover'), `Expected fit=cover in URL, got: ${url}`);
+		});
+
+		it('maps Astro fit values to Netlify equivalents', () => {
+			const cases = [
+				['contain', 'contain'],
+				['cover', 'cover'],
+				['fill', 'fill'],
+				['inside', 'contain'],
+				['outside', 'cover'],
+				['scale-down', 'contain'],
+			];
+			for (const [astroFit, netlifyFit] of cases) {
+				const url = getURL({
+					src: 'img.jpg',
+					width: 100,
+					height: 100,
+					fit: astroFit,
+				});
+				assert.ok(
+					url.includes(`fit=${netlifyFit}`),
+					`Expected fit=${netlifyFit} for astro fit="${astroFit}", got: ${url}`,
+				);
+			}
+		});
+
+		it('omits fit parameter when fit is none or unset', () => {
+			const withNone = getURL({
+				src: 'img.jpg',
+				width: 100,
+				height: 100,
+				fit: 'none',
+			});
+			assert.ok(
+				!withNone.includes('fit='),
+				`Expected no fit param for fit="none", got: ${withNone}`,
+			);
+
+			const withoutFit = getURL({ src: 'img.jpg', width: 100, height: 100 });
+			assert.ok(
+				!withoutFit.includes('fit='),
+				`Expected no fit param when unset, got: ${withoutFit}`,
+			);
+		});
+	});
+});
diff --git a/packages/integrations/netlify/test/functions/include-files.test.js b/packages/integrations/netlify/test/functions/include-files.test.js
deleted file mode 100644
index e54e116a78c3..000000000000
--- a/packages/integrations/netlify/test/functions/include-files.test.js
+++ /dev/null
@@ -1,184 +0,0 @@
-import * as assert from 'node:assert/strict';
-import { existsSync } from 'node:fs';
-import { after, before, describe, it } from 'node:test';
-import netlify from '@astrojs/netlify';
-import * as cheerio from 'cheerio';
-import { globSync } from 'tinyglobby';
-import { loadFixture } from '../../../../astro/test/test-utils.js';
-
-describe(
-	'Included vite assets files',
-	() => {
-		let fixture;
-
-		const root = new URL('./fixtures/includes/', import.meta.url);
-		const expectedCwd = new URL('.netlify/v1/functions/ssr/packages/integrations/netlify/', root);
-
-		const expectedAssetsInclude = ['./*.json'];
-		const excludedAssets = ['./files/exclude-asset.json'];
-
-		before(async () => {
-			fixture = await loadFixture({
-				root,
-				vite: {
-					assetsInclude: expectedAssetsInclude,
-				},
-				adapter: netlify({
-					excludeFiles: excludedAssets,
-				}),
-			});
-			await fixture.build();
-		});
-
-		it('Emits vite assets files', async () => {
-			for (const pattern of expectedAssetsInclude) {
-				const files = globSync(pattern);
-				for (const file of files) {
-					assert.ok(
-						existsSync(new URL(file, expectedCwd)),
-						`Expected file ${pattern} to exist in build`,
-					);
-				}
-			}
-		});
-
-		it('Does not include vite assets files when excluded', async () => {
-			for (const file of excludedAssets) {
-				assert.ok(
-					!existsSync(new URL(file, expectedCwd)),
-					`Expected file ${file} to not exist in build`,
-				);
-			}
-		});
-
-		after(async () => {
-			await fixture.clean();
-		});
-	},
-	{
-		timeout: 120000,
-	},
-);
-
-describe(
-	'Included files',
-	() => {
-		let fixture;
-
-		const root = new URL('./fixtures/includes/', import.meta.url);
-		const expectedCwd = new URL(
-			'.netlify/v1/functions/ssr/packages/integrations/netlify/test/functions/fixtures/includes/',
-			root,
-		);
-
-		const expectedFiles = [
-			'./files/include-this.txt',
-			'./files/also-this.csv',
-			'./files/subdirectory/and-this.csv',
-		];
-
-		before(async () => {
-			fixture = await loadFixture({
-				root,
-				adapter: netlify({
-					includeFiles: expectedFiles,
-				}),
-			});
-			await fixture.build();
-		});
-
-		it('Emits include files', async () => {
-			for (const file of expectedFiles) {
-				assert.ok(existsSync(new URL(file, expectedCwd)), `Expected file ${file} to exist`);
-			}
-		});
-
-		it('Can load included files correctly', async () => {
-			const entryURL = new URL(
-				'./fixtures/includes/.netlify/v1/functions/ssr/ssr.mjs',
-				import.meta.url,
-			);
-			const { default: handler } = await import(entryURL);
-			const resp = await handler(new Request('http://example.com/?file=include-this.txt'), {});
-			const html = await resp.text();
-			const $ = cheerio.load(html);
-			assert.equal($('h1').text(), 'hello');
-		});
-
-		it('Includes traced node modules with symlinks', async () => {
-			const expected = new URL(
-				'.netlify/v1/functions/ssr/node_modules/.pnpm/cowsay@1.6.0/node_modules/cowsay/cows/happy-whale.cow',
-				root,
-			);
-			assert.ok(existsSync(expected, 'Expected excluded file to exist in default build'));
-		});
-
-		after(async () => {
-			await fixture.clean();
-		});
-	},
-	{
-		timeout: 120000,
-	},
-);
-
-describe(
-	'Excluded files',
-	() => {
-		let fixture;
-
-		const root = new URL('./fixtures/includes/', import.meta.url);
-		const expectedCwd = new URL(
-			'.netlify/v1/functions/ssr/packages/integrations/netlify/test/functions/fixtures/includes/',
-			root,
-		);
-
-		const includeFiles = ['./files/**/*.txt'];
-		const excludedTxt = ['./files/subdirectory/not-this.txt', './files/subdirectory/or-this.txt'];
-		const excludeFiles = [...excludedTxt, '../../../../../../../node_modules/.pnpm/cowsay@*/**'];
-
-		before(async () => {
-			fixture = await loadFixture({
-				root,
-				adapter: netlify({
-					includeFiles: includeFiles,
-					excludeFiles: excludeFiles,
-				}),
-			});
-			await fixture.build();
-		});
-
-		it('Excludes traced node modules', async () => {
-			const expected = new URL(
-				'.netlify/v1/functions/ssr/node_modules/.pnpm/cowsay@1.6.0/node_modules/cowsay/cows/happy-whale.cow',
-				root,
-			);
-			assert.ok(!existsSync(expected), 'Expected excluded file to not exist in build');
-		});
-
-		it('Does not include files when excluded', async () => {
-			for (const pattern of includeFiles) {
-				const files = globSync(pattern, { ignore: excludedTxt });
-				for (const file of files) {
-					assert.ok(
-						existsSync(new URL(file, expectedCwd)),
-						`Expected file ${pattern} to exist in build`,
-					);
-				}
-			}
-			for (const file of excludedTxt) {
-				assert.ok(
-					!existsSync(new URL(file, expectedCwd)),
-					`Expected file ${file} to not exist in build`,
-				);
-			}
-		});
-
-		after(async () => {
-			await fixture.clean();
-		});
-	},
-	{
-		timeout: 120000,
-	},
-);
diff --git a/packages/integrations/netlify/test/functions/include-files.test.ts b/packages/integrations/netlify/test/functions/include-files.test.ts
new file mode 100644
index 000000000000..487298342eb5
--- /dev/null
+++ b/packages/integrations/netlify/test/functions/include-files.test.ts
@@ -0,0 +1,166 @@
+import * as assert from 'node:assert/strict';
+import { existsSync } from 'node:fs';
+import { after, before, describe, it } from 'node:test';
+import netlify from '@astrojs/netlify';
+import * as cheerio from 'cheerio';
+import { globSync } from 'tinyglobby';
+import { type Fixture, loadFixture } from '../../../../astro/test/test-utils.js';
+
+describe('Included vite assets files', { timeout: 120000 }, () => {
+	let fixture: Fixture;
+
+	const root = new URL('./fixtures/includes/', import.meta.url);
+	const expectedCwd = new URL('.netlify/v1/functions/ssr/packages/integrations/netlify/', root);
+
+	const expectedAssetsInclude = ['./*.json'];
+	const excludedAssets = ['./files/exclude-asset.json'];
+
+	before(async () => {
+		fixture = await loadFixture({
+			root,
+			vite: {
+				assetsInclude: expectedAssetsInclude,
+			},
+			adapter: netlify({
+				excludeFiles: excludedAssets,
+			}),
+		});
+		await fixture.build({});
+	});
+
+	it('Emits vite assets files', async () => {
+		for (const pattern of expectedAssetsInclude) {
+			const files = globSync(pattern);
+			for (const file of files) {
+				assert.ok(
+					existsSync(new URL(file, expectedCwd)),
+					`Expected file ${pattern} to exist in build`,
+				);
+			}
+		}
+	});
+
+	it('Does not include vite assets files when excluded', async () => {
+		for (const file of excludedAssets) {
+			assert.ok(
+				!existsSync(new URL(file, expectedCwd)),
+				`Expected file ${file} to not exist in build`,
+			);
+		}
+	});
+
+	after(async () => {
+		await fixture.clean();
+	});
+});
+
+describe('Included files', { timeout: 120000 }, () => {
+	let fixture: Fixture;
+
+	const root = new URL('./fixtures/includes/', import.meta.url);
+	const expectedCwd = new URL(
+		'.netlify/v1/functions/ssr/packages/integrations/netlify/test/functions/fixtures/includes/',
+		root,
+	);
+
+	const expectedFiles = [
+		'./files/include-this.txt',
+		'./files/also-this.csv',
+		'./files/subdirectory/and-this.csv',
+	];
+
+	before(async () => {
+		fixture = await loadFixture({
+			root,
+			adapter: netlify({
+				includeFiles: expectedFiles,
+			}),
+		});
+		await fixture.build({});
+	});
+
+	it('Emits include files', async () => {
+		for (const file of expectedFiles) {
+			assert.ok(existsSync(new URL(file, expectedCwd)), `Expected file ${file} to exist`);
+		}
+	});
+
+	it('Can load included files correctly', async () => {
+		const entryURL = new URL(
+			'./fixtures/includes/.netlify/v1/functions/ssr/ssr.mjs',
+			import.meta.url,
+		);
+		const { default: handler } = await import(entryURL.href);
+		const resp = await handler(new Request('http://example.com/?file=include-this.txt'), {});
+		const html = await resp.text();
+		const $ = cheerio.load(html);
+		assert.equal($('h1').text(), 'hello');
+	});
+
+	it('Includes traced node modules with symlinks', async () => {
+		const expected = new URL(
+			'.netlify/v1/functions/ssr/node_modules/.pnpm/cowsay@1.6.0/node_modules/cowsay/cows/happy-whale.cow',
+			root,
+		);
+		assert.ok(existsSync(expected), 'Expected excluded file to exist in default build');
+	});
+
+	after(async () => {
+		await fixture.clean();
+	});
+});
+
+describe('Excluded files', { timeout: 120000 }, () => {
+	let fixture: Fixture;
+
+	const root = new URL('./fixtures/includes/', import.meta.url);
+	const expectedCwd = new URL(
+		'.netlify/v1/functions/ssr/packages/integrations/netlify/test/functions/fixtures/includes/',
+		root,
+	);
+
+	const includeFiles = ['./files/**/*.txt'];
+	const excludedTxt = ['./files/subdirectory/not-this.txt', './files/subdirectory/or-this.txt'];
+	const excludeFiles = [...excludedTxt, '../../../../../../../node_modules/.pnpm/cowsay@*/**'];
+
+	before(async () => {
+		fixture = await loadFixture({
+			root,
+			adapter: netlify({
+				includeFiles: includeFiles,
+				excludeFiles: excludeFiles,
+			}),
+		});
+		await fixture.build({});
+	});
+
+	it('Excludes traced node modules', async () => {
+		const expected = new URL(
+			'.netlify/v1/functions/ssr/node_modules/.pnpm/cowsay@1.6.0/node_modules/cowsay/cows/happy-whale.cow',
+			root,
+		);
+		assert.ok(!existsSync(expected), 'Expected excluded file to not exist in build');
+	});
+
+	it('Does not include files when excluded', async () => {
+		for (const pattern of includeFiles) {
+			const files = globSync(pattern, { ignore: excludedTxt });
+			for (const file of files) {
+				assert.ok(
+					existsSync(new URL(file, expectedCwd)),
+					`Expected file ${pattern} to exist in build`,
+				);
+			}
+		}
+		for (const file of excludedTxt) {
+			assert.ok(
+				!existsSync(new URL(file, expectedCwd)),
+				`Expected file ${file} to not exist in build`,
+			);
+		}
+	});
+
+	after(async () => {
+		await fixture.clean();
+	});
+});
diff --git a/packages/integrations/netlify/test/functions/redirects.test.js b/packages/integrations/netlify/test/functions/redirects.test.js
deleted file mode 100644
index 2c55aecb9ec5..000000000000
--- a/packages/integrations/netlify/test/functions/redirects.test.js
+++ /dev/null
@@ -1,68 +0,0 @@
-import * as assert from 'node:assert/strict';
-import { createServer } from 'node:http';
-import { before, describe, it } from 'node:test';
-import { loadFixture } from '../../../../astro/test/test-utils.js';
-
-describe(
-	'SSR - Redirects',
-	() => {
-		let fixture;
-
-		before(async () => {
-			fixture = await loadFixture({ root: new URL('./fixtures/redirects/', import.meta.url) });
-			await fixture.build();
-		});
-
-		it('Creates a redirects file', async () => {
-			const redirects = await fixture.readFile('./_redirects');
-			const parts = redirects.split(/\s+/);
-			// based on https://github.com/withastro/astro/issues/16030 for the default option `trailingSlash: 'ignore'` both variants should be generated
-			assert.deepEqual(parts, ['', '/other/', '/', '301', '/other', '/', '301', '']);
-		});
-
-		it('Does not create .html files', async () => {
-			let hasErrored = false;
-			try {
-				await fixture.readFile('/other/index.html');
-			} catch {
-				hasErrored = true;
-			}
-			assert.equal(hasErrored, true, 'this file should not exist');
-		});
-
-		it('renders static 404 page', async () => {
-			const entryURL = new URL(
-				'./fixtures/redirects/.netlify/v1/functions/ssr/ssr.mjs',
-				import.meta.url,
-			);
-			const { default: handler } = await import(entryURL);
-			const resp = await handler(new Request('http://example.com/nonexistant-page'), {});
-			assert.equal(resp.status, 404);
-			assert.equal(resp.headers.get('content-type'), 'text/html; charset=utf-8');
-			const text = await resp.text();
-			assert.equal(text.includes('This is my static 404 page'), true);
-		});
-
-		it('does not pass through 404 request', async () => {
-			let testServerCalls = 0;
-			const testServer = createServer((_req, res) => {
-				testServerCalls++;
-				res.writeHead(200);
-				res.end();
-			});
-			testServer.listen(5678);
-			const entryURL = new URL(
-				'./fixtures/redirects/.netlify/v1/functions/ssr/ssr.mjs',
-				import.meta.url,
-			);
-			const { default: handler } = await import(entryURL);
-			const resp = await handler(new Request('http://localhost:5678/nonexistant-page'), {});
-			assert.equal(resp.status, 404);
-			assert.equal(testServerCalls, 0);
-			testServer.close();
-		});
-	},
-	{
-		timeout: 120000,
-	},
-);
diff --git a/packages/integrations/netlify/test/functions/redirects.test.ts b/packages/integrations/netlify/test/functions/redirects.test.ts
new file mode 100644
index 000000000000..9f983ea5cabc
--- /dev/null
+++ b/packages/integrations/netlify/test/functions/redirects.test.ts
@@ -0,0 +1,62 @@
+import * as assert from 'node:assert/strict';
+import { createServer } from 'node:http';
+import { before, describe, it } from 'node:test';
+import { type Fixture, loadFixture } from '../../../../astro/test/test-utils.js';
+
+describe('SSR - Redirects', { timeout: 120000 }, () => {
+	let fixture: Fixture;
+
+	before(async () => {
+		fixture = await loadFixture({ root: new URL('./fixtures/redirects/', import.meta.url) });
+		await fixture.build({});
+	});
+
+	it('Creates a redirects file', async () => {
+		const redirects = await fixture.readFile('./_redirects');
+		const parts = redirects.split(/\s+/);
+		// based on https://github.com/withastro/astro/issues/16030 for the default option `trailingSlash: 'ignore'` both variants should be generated
+		assert.deepEqual(parts, ['', '/other/', '/', '301', '/other', '/', '301', '']);
+	});
+
+	it('Does not create .html files', async () => {
+		let hasErrored = false;
+		try {
+			await fixture.readFile('/other/index.html');
+		} catch {
+			hasErrored = true;
+		}
+		assert.equal(hasErrored, true, 'this file should not exist');
+	});
+
+	it('renders static 404 page', async () => {
+		const entryURL = new URL(
+			'./fixtures/redirects/.netlify/v1/functions/ssr/ssr.mjs',
+			import.meta.url,
+		);
+		const { default: handler } = await import(entryURL.href);
+		const resp = await handler(new Request('http://example.com/nonexistant-page'), {});
+		assert.equal(resp.status, 404);
+		assert.equal(resp.headers.get('content-type'), 'text/html; charset=utf-8');
+		const text = await resp.text();
+		assert.equal(text.includes('This is my static 404 page'), true);
+	});
+
+	it('does not pass through 404 request', async () => {
+		let testServerCalls = 0;
+		const testServer = createServer((_req, res) => {
+			testServerCalls++;
+			res.writeHead(200);
+			res.end();
+		});
+		testServer.listen(5678);
+		const entryURL = new URL(
+			'./fixtures/redirects/.netlify/v1/functions/ssr/ssr.mjs',
+			import.meta.url,
+		);
+		const { default: handler } = await import(entryURL.href);
+		const resp = await handler(new Request('http://localhost:5678/nonexistant-page'), {});
+		assert.equal(resp.status, 404);
+		assert.equal(testServerCalls, 0);
+		testServer.close();
+	});
+});
diff --git a/packages/integrations/netlify/test/functions/sessions.test.js b/packages/integrations/netlify/test/functions/sessions.test.ts
similarity index 90%
rename from packages/integrations/netlify/test/functions/sessions.test.js
rename to packages/integrations/netlify/test/functions/sessions.test.ts
index 7b41cb129648..89d4a1b8d432 100644
--- a/packages/integrations/netlify/test/functions/sessions.test.js
+++ b/packages/integrations/netlify/test/functions/sessions.test.ts
@@ -1,10 +1,9 @@
-// @ts-check
 import assert from 'node:assert/strict';
 import { mkdir, rm } from 'node:fs/promises';
 import { after, before, describe, it } from 'node:test';
 import { BlobsServer } from '@netlify/blobs/server';
 import * as devalue from 'devalue';
-import { loadFixture } from '../../../../astro/test/test-utils.js';
+import { type Fixture, loadFixture } from '../../../../astro/test/test-utils.js';
 import netlify from '../../dist/index.js';
 import { sessionDrivers } from 'astro/config';
 
@@ -14,11 +13,9 @@ const dataDir = '.netlify/sessions';
 
 describe('Astro.session', () => {
 	describe('Production', () => {
-		/** @type {import('../../../../astro/test/test-utils.js').Fixture} */
-		let fixture;
+		let fixture: Fixture;
 
-		/** @type {BlobsServer} */
-		let blobServer;
+		let blobServer: BlobsServer;
 		before(async () => {
 			process.env.NETLIFY = '1';
 			await rm(dataDir, { recursive: true, force: true }).catch(() => {});
@@ -35,6 +32,7 @@ describe('Astro.session', () => {
 				output: 'server',
 				adapter: netlify(),
 				session: {
+					// @ts-ignore - session driver types are complex generics
 					driver: sessionDrivers.netlifyBlobs({
 						name: 'test',
 						uncachedEdgeURL: `http://localhost:8971`,
@@ -52,17 +50,12 @@ describe('Astro.session', () => {
 			const mod = await import(entryURL.href);
 			handler = mod.default;
 		});
-		/** @type {(request: Request, options: {}) => Promise<Response>} */
-		let handler;
+		let handler: (request: Request, options: Record<string, unknown>) => Promise<Response>;
 		after(async () => {
 			await blobServer.stop();
 			delete process.env.NETLIFY;
 		});
-		/**
-		 * @param {string} path
-		 * @param {RequestInit} requestInit
-		 */
-		function fetchResponse(path, requestInit) {
+		function fetchResponse(path: string, requestInit: RequestInit) {
 			return handler(new Request(new URL(path, 'http://example.com'), requestInit), {});
 		}
 
diff --git a/packages/integrations/netlify/test/functions/skew-protection.test.js b/packages/integrations/netlify/test/functions/skew-protection.test.js
deleted file mode 100644
index ee5f8c840689..000000000000
--- a/packages/integrations/netlify/test/functions/skew-protection.test.js
+++ /dev/null
@@ -1,70 +0,0 @@
-import * as assert from 'node:assert/strict';
-import { readFile } from 'node:fs/promises';
-import { before, describe, it } from 'node:test';
-import { loadFixture } from '../../../../astro/test/test-utils.js';
-
-describe(
-	'Skew Protection',
-	() => {
-		let fixture;
-
-		before(async () => {
-			// Set DEPLOY_ID env var for the test
-			process.env.DEPLOY_ID = 'test-deploy-123';
-
-			fixture = await loadFixture({
-				root: new URL('./fixtures/skew-protection/', import.meta.url),
-			});
-			await fixture.build();
-
-			// Clean up
-			delete process.env.DEPLOY_ID;
-		});
-
-		it('Server islands inline adapter headers', async () => {
-			// Render a page with server islands and check the HTML contains inline headers
-			const entryURL = new URL(
-				'./fixtures/skew-protection/.netlify/v1/functions/ssr/ssr.mjs',
-				import.meta.url,
-			);
-			const { default: handler } = await import(entryURL);
-			const resp = await handler(new Request('http://example.com/server-island'), {});
-			const html = await resp.text();
-
-			// Check that the HTML contains the inline headers in the server island script
-			// Should have something like: const headers = new Headers({"X-Netlify-Deploy-ID":"test-deploy-123"});
-			assert.ok(
-				html.includes('test-deploy-123'),
-				'Expected server island HTML to include deploy ID in inline script',
-			);
-		});
-
-		it('Manifest contains internalFetchHeaders', async () => {
-			// The manifest is embedded in the build output
-			// Check the manifest file which contains the serialized manifest
-			const manifestURL = new URL(
-				'./fixtures/skew-protection/.netlify/build/chunks/',
-				import.meta.url,
-			);
-
-			// Find the manifest file (it has a hash in the name)
-			const { readdir } = await import('node:fs/promises');
-			const files = await readdir(manifestURL);
-			let found = false;
-			for (const file of files) {
-				const contents = await readFile(new URL(file, manifestURL), 'utf-8');
-				if (contents.includes('"internalFetchHeaders":{"X-Netlify-Deploy-ID":"test-deploy-123"}')) {
-					found = true;
-					break;
-				}
-			}
-			assert.ok(
-				found,
-				'Manifest should include internalFetchHeaders field with the correct deploy ID value',
-			);
-		});
-	},
-	{
-		timeout: 120000,
-	},
-);
diff --git a/packages/integrations/netlify/test/functions/skew-protection.test.ts b/packages/integrations/netlify/test/functions/skew-protection.test.ts
new file mode 100644
index 000000000000..e2dec88abfcf
--- /dev/null
+++ b/packages/integrations/netlify/test/functions/skew-protection.test.ts
@@ -0,0 +1,64 @@
+import * as assert from 'node:assert/strict';
+import { readFile } from 'node:fs/promises';
+import { before, describe, it } from 'node:test';
+import { type Fixture, loadFixture } from '../../../../astro/test/test-utils.js';
+
+describe('Skew Protection', { timeout: 120000 }, () => {
+	let fixture: Fixture;
+
+	before(async () => {
+		// Set DEPLOY_ID env var for the test
+		process.env.DEPLOY_ID = 'test-deploy-123';
+
+		fixture = await loadFixture({
+			root: new URL('./fixtures/skew-protection/', import.meta.url),
+		});
+		await fixture.build({});
+
+		// Clean up
+		delete process.env.DEPLOY_ID;
+	});
+
+	it('Server islands inline adapter headers', async () => {
+		// Render a page with server islands and check the HTML contains inline headers
+		const entryURL = new URL(
+			'./fixtures/skew-protection/.netlify/v1/functions/ssr/ssr.mjs',
+			import.meta.url,
+		);
+		const { default: handler } = await import(entryURL.href);
+		const resp = await handler(new Request('http://example.com/server-island'), {});
+		const html = await resp.text();
+
+		// Check that the HTML contains the inline headers in the server island script
+		// Should have something like: const headers = new Headers({"X-Netlify-Deploy-ID":"test-deploy-123"});
+		assert.ok(
+			html.includes('test-deploy-123'),
+			'Expected server island HTML to include deploy ID in inline script',
+		);
+	});
+
+	it('Manifest contains internalFetchHeaders', async () => {
+		// The manifest is embedded in the build output
+		// Check the manifest file which contains the serialized manifest
+		const manifestURL = new URL(
+			'./fixtures/skew-protection/.netlify/build/chunks/',
+			import.meta.url,
+		);
+
+		// Find the manifest file (it has a hash in the name)
+		const { readdir } = await import('node:fs/promises');
+		const files = await readdir(manifestURL);
+		let found = false;
+		for (const file of files) {
+			const contents = await readFile(new URL(file, manifestURL), 'utf-8');
+			if (contents.includes('"internalFetchHeaders":{"X-Netlify-Deploy-ID":"test-deploy-123"}')) {
+				found = true;
+				break;
+			}
+		}
+		assert.ok(
+			found,
+			'Manifest should include internalFetchHeaders field with the correct deploy ID value',
+		);
+	});
+});
diff --git a/packages/integrations/netlify/test/hosted/hosted.test.js b/packages/integrations/netlify/test/hosted/hosted.test.ts
similarity index 94%
rename from packages/integrations/netlify/test/hosted/hosted.test.js
rename to packages/integrations/netlify/test/hosted/hosted.test.ts
index 3bc9349f960b..fb671afb4008 100644
--- a/packages/integrations/netlify/test/hosted/hosted.test.js
+++ b/packages/integrations/netlify/test/hosted/hosted.test.ts
@@ -24,6 +24,6 @@ describe('Hosted Netlify Tests', () => {
 
 		const responseTwo = await fetch(`${NETLIFY_TEST_URL}/time`).then((res) => res.text());
 
-		assert.notEqual(responseOne.body, responseTwo.body);
+		assert.notEqual(responseOne, responseTwo);
 	});
 });
diff --git a/packages/integrations/netlify/test/static/headers.test.js b/packages/integrations/netlify/test/static/headers.test.ts
similarity index 81%
rename from packages/integrations/netlify/test/static/headers.test.js
rename to packages/integrations/netlify/test/static/headers.test.ts
index 5c1400098b10..d777cbc824ae 100644
--- a/packages/integrations/netlify/test/static/headers.test.js
+++ b/packages/integrations/netlify/test/static/headers.test.ts
@@ -1,13 +1,13 @@
 import * as assert from 'node:assert/strict';
 import { before, describe, it } from 'node:test';
-import { loadFixture } from '../../../../astro/test/test-utils.js';
+import { type Fixture, loadFixture } from '../../../../astro/test/test-utils.js';
 
 describe('SSG - headers', () => {
-	let fixture;
+	let fixture: Fixture;
 
 	before(async () => {
 		fixture = await loadFixture({ root: new URL('./fixtures/redirects/', import.meta.url) });
-		await fixture.build();
+		await fixture.build({});
 	});
 
 	it('Generates headers for static assets', async () => {
diff --git a/packages/integrations/netlify/test/static/image-missing-dimension.test.js b/packages/integrations/netlify/test/static/image-missing-dimension.test.ts
similarity index 92%
rename from packages/integrations/netlify/test/static/image-missing-dimension.test.js
rename to packages/integrations/netlify/test/static/image-missing-dimension.test.ts
index 932958ad399d..3519081e1160 100644
--- a/packages/integrations/netlify/test/static/image-missing-dimension.test.js
+++ b/packages/integrations/netlify/test/static/image-missing-dimension.test.ts
@@ -9,12 +9,12 @@ describe('Image validation when is not size specification in netlify.', () => {
 		});
 
 		try {
-			await fixture.build();
+			await fixture.build({});
 			assert.fail();
 		} catch (e) {
 			// check the error image about missing image dimension
 			assert.match(
-				e.name,
+				(e as Error).name,
 				/MissingImageDimension/,
 				`Build failed but not with the expected "MissingImageDimension"`,
 			);
diff --git a/packages/integrations/netlify/test/static/redirects.test.js b/packages/integrations/netlify/test/static/redirects.test.ts
similarity index 85%
rename from packages/integrations/netlify/test/static/redirects.test.js
rename to packages/integrations/netlify/test/static/redirects.test.ts
index 9e9d0c87298e..e541efa58117 100644
--- a/packages/integrations/netlify/test/static/redirects.test.js
+++ b/packages/integrations/netlify/test/static/redirects.test.ts
@@ -1,13 +1,13 @@
 import * as assert from 'node:assert/strict';
 import { before, describe, it } from 'node:test';
-import { loadFixture } from '../../../../astro/test/test-utils.js';
+import { type Fixture, loadFixture } from '../../../../astro/test/test-utils.js';
 
 describe('SSG - Redirects', () => {
-	let fixture;
+	let fixture: Fixture;
 
 	before(async () => {
 		fixture = await loadFixture({ root: new URL('./fixtures/redirects/', import.meta.url) });
-		await fixture.build();
+		await fixture.build({});
 	});
 
 	it('Creates a redirects file', async () => {
diff --git a/packages/integrations/netlify/test/static/static-headers.test.js b/packages/integrations/netlify/test/static/static-headers.test.ts
similarity index 86%
rename from packages/integrations/netlify/test/static/static-headers.test.js
rename to packages/integrations/netlify/test/static/static-headers.test.ts
index a5b7014894b0..5a478eccfed7 100644
--- a/packages/integrations/netlify/test/static/static-headers.test.js
+++ b/packages/integrations/netlify/test/static/static-headers.test.ts
@@ -1,14 +1,14 @@
 import * as assert from 'node:assert/strict';
 import { existsSync, readdirSync } from 'node:fs';
 import { before, describe, it } from 'node:test';
-import { loadFixture } from '../../../../astro/test/test-utils.js';
+import { type Fixture, loadFixture } from '../../../../astro/test/test-utils.js';
 
 describe('Static headers', () => {
-	let fixture;
+	let fixture: Fixture;
 
 	before(async () => {
 		fixture = await loadFixture({ root: new URL('./fixtures/static-headers/', import.meta.url) });
-		await fixture.build();
+		await fixture.build({});
 	});
 
 	it('SSR function is generated when server islands are used with output: static', async () => {
@@ -23,7 +23,7 @@ describe('Static headers', () => {
 	it('CSP headers are added when CSP is enabled', async () => {
 		const config = await fixture.readFile('../.netlify/v1/config.json');
 		const headers = JSON.parse(config).headers;
-		const index = headers.find((x) => x.for === '/');
+		const index = headers.find((x: { for: string }) => x.for === '/');
 
 		assert.notEqual(index, undefined, 'the index must have CSP headers');
 		assert.notEqual(
diff --git a/packages/integrations/netlify/tsconfig.test.json b/packages/integrations/netlify/tsconfig.test.json
new file mode 100644
index 000000000000..e8d5292cf781
--- /dev/null
+++ b/packages/integrations/netlify/tsconfig.test.json
@@ -0,0 +1,14 @@
+{
+  "extends": "../../../tsconfig.base.json",
+  "include": ["test/**/*.ts"],
+  "exclude": ["test/fixtures/**", "test/*/fixtures/**", "test/hosted/hosted-astro-project/**"],
+  "compilerOptions": {
+    "noEmit": true,
+    "allowJs": true,
+    "noUnusedLocals": false,
+    "noUnusedParameters": false,
+    "rewriteRelativeImportExtensions": true,
+    "rootDir": "."
+  },
+  "references": [{ "path": "../../astro/tsconfig.test.json" }]
+}