docs: update Vitest instructions for jest-dom

docs/svelte-testing-library/setup.mdx

@@ -66,6 +66,28 @@ with any testing framework and runner you're comfortable with.
  ```js
  import '@testing-library/jest-dom';
  ```
+
+ 5.3 Set up automatic imports (optional)
+
+ To import this automatically in _every_ test file, create a new file containing the import statement from the previous step, then add the file to the `setupFiles` array in the `vitest.config.ts` (in this case, the file is `vitest.include.jsdom.ts` in the project root)
+
+ ```js
+ import { defineConfig } from 'vitest/config';
+ import { svelte } from '@sveltejs/vite-plugin-svelte';
+
+ export default defineConfig({
+ plugins: [svelte({ hot: !process.env.VITEST })],
+ test: {
+ include: ['src/**/*.{test,spec}.{js,mjs,cjs,ts,mts,cts,jsx,tsx}'],
+ globals: true,
+ environment: 'jsdom',
+ setupFiles: [
+ './vitest.include.jsdom.ts'
+ ]
+ }
+ });
+
+ ```
 
 6. Create your component and a test file (checkout the rest of the docs to see how)
  and run the following command to run the tests.