adding basic test coverage for cached images

packages/integrations/image/test/image-ssg.test.js

@@ -1,6 +1,7 @@
 import { expect } from 'chai';
 import * as cheerio from 'cheerio';
 import sizeOf from 'image-size';
+import fs from 'fs/promises';
 import { fileURLToPath } from 'url';
 import { loadFixture } from './test-utils.js';
 
@@ -253,14 +254,17 @@ describe('SSG images - build', function () {
 			size: { width: 544, height: 184, type: 'jpg' },
 		},
 	].forEach(({ title, id, regex, size }) => {
-		it(title, () => {
+		it(title, async () => {
 			const image = $(id);
 
 			expect(image.attr('src')).to.match(regex);
 			expect(image.attr('width')).to.equal(size.width.toString());
 			expect(image.attr('height')).to.equal(size.height.toString());
 
 			verifyImage(image.attr('src'), size);
+
+			const url = new URL('./fixtures/basic-image/node_modules/.astro/image' + image.attr('src'), import.meta.url);
+			expect(await fs.stat(url), 'transformed image was cached').to.not.be.undefined;
 		});
 	});
 });