diff --git a/packages/astro/test/core-image-service.test.js b/packages/astro/test/core-image-service.test.js
deleted file mode 100644
index 60b04a1762ef..000000000000
--- a/packages/astro/test/core-image-service.test.js
+++ /dev/null
@@ -1,204 +0,0 @@
-import assert from 'node:assert/strict';
-import { after, before, describe, it } from 'node:test';
-import { removeDir } from '@astrojs/internal-helpers/fs';
-import * as cheerio from 'cheerio';
-import { lookup as probe } from '../dist/assets/utils/vendor/image-size/lookup.js';
-import { loadFixture } from './test-utils.js';
-
-async function getImageDimensionsFromFixture(fixture, path) {
-	/** @type { Response } */
-	const res = await fixture.fetch(path instanceof URL ? path.pathname + path.search : path);
-	const buffer = await res.arrayBuffer();
-	const { width, height } = await probe(new Uint8Array(buffer));
-	return { width, height };
-}
-
-async function getImageDimensionsFromLocalFile(fixture, path) {
-	const buffer = await fixture.readFile(path, null);
-	const { width, height } = await probe(new Uint8Array(buffer));
-	return { width, height };
-}
-
-describe('astro image service', () => {
-	/** @type {import('./test-utils').Fixture} */
-	let fixture;
-
-	describe('dev image service', () => {
-		/** @type {import('./test-utils').DevServer} */
-		let devServer;
-
-		before(async () => {
-			fixture = await loadFixture({
-				root: './fixtures/core-image-layout/',
-				image: {
-					domains: ['unsplash.com'],
-				},
-			});
-
-			devServer = await fixture.startDevServer({});
-		});
-
-		after(async () => {
-			await devServer.stop();
-		});
-
-		describe('generated images', () => {
-			let $;
-			let src;
-			before(async () => {
-				const res = await fixture.fetch('/fit');
-				const html = await res.text();
-				$ = cheerio.load(html);
-				let $img = $('#local-both img');
-				src = new URL($img.attr('src'), 'http://localhost').href;
-			});
-
-			it('generates correct width and height when both are provided', async () => {
-				const url = new URL(src);
-				const { width, height } = await getImageDimensionsFromFixture(fixture, url);
-				assert.equal(width, 300);
-				assert.equal(height, 400);
-			});
-
-			it('generates correct height when only width is provided', async () => {
-				const url = new URL(src);
-				url.searchParams.delete('h');
-				const { width, height } = await getImageDimensionsFromFixture(fixture, url);
-				assert.equal(width, 300);
-				assert.equal(height, 200);
-			});
-
-			it('generates correct width when only height is provided', async () => {
-				const url = new URL(src);
-				url.searchParams.delete('w');
-				url.searchParams.set('h', '400');
-				const { width, height } = await getImageDimensionsFromFixture(fixture, url);
-				assert.equal(width, 600);
-				assert.equal(height, 400);
-			});
-
-			it('preserves aspect ratio when fit=inside', async () => {
-				const url = new URL(src);
-				url.searchParams.set('fit', 'inside');
-				const { width, height } = await getImageDimensionsFromFixture(fixture, url);
-				assert.equal(width, 300);
-				assert.equal(height, 200);
-			});
-
-			it('preserves aspect ratio when fit=contain', async () => {
-				const url = new URL(src);
-				url.searchParams.set('fit', 'contain');
-				const { width, height } = await getImageDimensionsFromFixture(fixture, url);
-				assert.equal(width, 300);
-				assert.equal(height, 200);
-			});
-
-			it('preserves aspect ratio when fit=outside', async () => {
-				const url = new URL(src);
-				url.searchParams.set('fit', 'outside');
-				const { width, height } = await getImageDimensionsFromFixture(fixture, url);
-				assert.equal(width, 600);
-				assert.equal(height, 400);
-			});
-			const originalWidth = 2316;
-			const originalHeight = 1544;
-			it('does not upscale image if requested size is larger than original', async () => {
-				const url = new URL(src);
-				url.searchParams.set('w', '3000');
-				url.searchParams.set('h', '2000');
-				const { width, height } = await getImageDimensionsFromFixture(fixture, url);
-				assert.equal(width, originalWidth);
-				assert.equal(height, originalHeight);
-			});
-
-			it('does not upscale image if requested size is larger than original and fit is unset', async () => {
-				const url = new URL(src);
-				url.searchParams.set('w', '3000');
-				url.searchParams.set('h', '2000');
-				url.searchParams.delete('fit');
-				const { width, height } = await getImageDimensionsFromFixture(fixture, url);
-				assert.equal(width, originalWidth);
-				assert.equal(height, originalHeight);
-			});
-
-			it('does not upscale if only one dimension is provided and fit is set', async () => {
-				const url = new URL(src);
-				url.searchParams.set('w', '3000');
-				url.searchParams.delete('h');
-				url.searchParams.set('fit', 'cover');
-				const { width, height } = await getImageDimensionsFromFixture(fixture, url);
-				assert.equal(width, originalWidth);
-				assert.equal(height, originalHeight);
-			});
-		});
-	});
-
-	describe('build image service', () => {
-		before(async () => {
-			fixture = await loadFixture({
-				root: './fixtures/core-image-layout/',
-			});
-			removeDir(new URL('./fixtures/core-image-ssg/node_modules/.astro', import.meta.url));
-
-			await fixture.build();
-		});
-
-		describe('generated images', () => {
-			let $;
-			before(async () => {
-				const html = await fixture.readFile('/build/index.html');
-				$ = cheerio.load(html);
-			});
-
-			it('generates correct width and height when both are provided', async () => {
-				const path = $('.both img').attr('src');
-				const { width, height } = await getImageDimensionsFromLocalFile(fixture, path);
-				assert.equal(width, 300);
-				assert.equal(height, 400);
-			});
-
-			it('generates correct height when only width is provided', async () => {
-				const path = $('.width-only img').attr('src');
-				const { width, height } = await getImageDimensionsFromLocalFile(fixture, path);
-				assert.equal(width, 300);
-				assert.equal(height, 200);
-			});
-
-			it('generates correct width when only height is provided', async () => {
-				const path = $('.height-only img').attr('src');
-				const { width, height } = await getImageDimensionsFromLocalFile(fixture, path);
-				assert.equal(width, 600);
-				assert.equal(height, 400);
-			});
-
-			it('preserves aspect ratio when fit=inside', async () => {
-				const path = $('.fit-inside img').attr('src');
-				const { width, height } = await getImageDimensionsFromLocalFile(fixture, path);
-				assert.equal(width, 300);
-				assert.equal(height, 200);
-			});
-
-			it('preserves aspect ratio when fit=contain', async () => {
-				const path = $('.fit-contain img').attr('src');
-				const { width, height } = await getImageDimensionsFromLocalFile(fixture, path);
-				assert.equal(width, 300);
-				assert.equal(height, 200);
-			});
-
-			it('preserves aspect ratio when fit=outside', async () => {
-				const path = $('.fit-outside img').attr('src');
-				const { width, height } = await getImageDimensionsFromLocalFile(fixture, path);
-				assert.equal(width, 600);
-				assert.equal(height, 400);
-			});
-			const originalWidth = 2316;
-			const originalHeight = 1544;
-			it('does not upscale image if requested size is larger than original', async () => {
-				const path = $('.too-large img').attr('src');
-				const { width, height } = await getImageDimensionsFromLocalFile(fixture, path);
-				assert.equal(width, originalWidth);
-				assert.equal(height, originalHeight);
-			});
-		});
-	});
-});
diff --git a/packages/astro/test/units/assets/600x400.jpg b/packages/astro/test/units/assets/600x400.jpg
new file mode 100644
index 000000000000..1388b0116bc5
Binary files /dev/null and b/packages/astro/test/units/assets/600x400.jpg differ
diff --git a/packages/astro/test/units/assets/image-service.test.js b/packages/astro/test/units/assets/image-service.test.js
new file mode 100644
index 000000000000..61e4702cdf82
--- /dev/null
+++ b/packages/astro/test/units/assets/image-service.test.js
@@ -0,0 +1,83 @@
+import assert from 'node:assert/strict';
+import { readFile } from 'node:fs/promises';
+import { before, describe, it } from 'node:test';
+import { lookup as probe } from '../../../dist/assets/utils/vendor/image-size/lookup.js';
+
+// Small local image (600×400) to keep transforms fast without depending on external fixtures
+const FIXTURE_IMAGE = new URL('./600x400.jpg', import.meta.url);
+const ORIGINAL_WIDTH = 600;
+const ORIGINAL_HEIGHT = 400;
+
+describe('sharp image service', async () => {
+	const sharpService = (await import('../../../dist/assets/services/sharp.js')).default;
+
+	const config = { service: { entrypoint: '', config: {} } };
+
+	let inputBuffer;
+	before(async () => {
+		inputBuffer = new Uint8Array(await readFile(FIXTURE_IMAGE));
+	});
+
+	async function transform(opts) {
+		const { data } = await sharpService.transform(
+			inputBuffer,
+			{ src: 'penguin.jpg', format: 'webp', ...opts },
+			config,
+		);
+		return probe(data);
+	}
+
+	it('generates correct width and height when both are provided', async () => {
+		const { width, height } = await transform({ width: 300, height: 400, fit: 'cover' });
+		assert.equal(width, 300);
+		assert.equal(height, 400);
+	});
+
+	it('generates correct height when only width is provided', async () => {
+		const { width, height } = await transform({ width: 300 });
+		assert.equal(width, 300);
+		assert.equal(height, 200);
+	});
+
+	it('generates correct width when only height is provided', async () => {
+		const { width, height } = await transform({ height: 400 });
+		assert.equal(width, 600);
+		assert.equal(height, 400);
+	});
+
+	it('preserves aspect ratio when fit=inside', async () => {
+		const { width, height } = await transform({ width: 300, height: 400, fit: 'inside' });
+		assert.equal(width, 300);
+		assert.equal(height, 200);
+	});
+
+	it('preserves aspect ratio when fit=contain', async () => {
+		const { width, height } = await transform({ width: 300, height: 400, fit: 'contain' });
+		assert.equal(width, 300);
+		assert.equal(height, 200);
+	});
+
+	it('preserves aspect ratio when fit=outside', async () => {
+		const { width, height } = await transform({ width: 300, height: 400, fit: 'outside' });
+		assert.equal(width, 600);
+		assert.equal(height, 400);
+	});
+
+	it('does not upscale image if requested size is larger than original', async () => {
+		const { width, height } = await transform({ width: 3000, height: 2000, fit: 'cover' });
+		assert.equal(width, ORIGINAL_WIDTH);
+		assert.equal(height, ORIGINAL_HEIGHT);
+	});
+
+	it('does not upscale image if requested size is larger than original and fit is unset', async () => {
+		const { width, height } = await transform({ width: 3000, height: 2000 });
+		assert.equal(width, ORIGINAL_WIDTH);
+		assert.equal(height, ORIGINAL_HEIGHT);
+	});
+
+	it('does not upscale if only one dimension is provided and fit is set', async () => {
+		const { width, height } = await transform({ width: 3000, fit: 'cover' });
+		assert.equal(width, ORIGINAL_WIDTH);
+		assert.equal(height, ORIGINAL_HEIGHT);
+	});
+});