add separate test suite

Author: Rich-Harris

packages/svelte/tests/print/samples/basic/input.svelte

@@ -0,0 +1,7 @@
+<script>
+	let name = 'world'
+</script>
+
+<h1>
+	Hello {name}!
+</h1>

packages/svelte/tests/print/samples/basic/output.svelte

@@ -0,0 +1,5 @@
+<script>
+	let name = 'world';
+</script>
+
+<h1>Hello {name}!</h1>

packages/svelte/tests/print/test.ts

@@ -0,0 +1,32 @@
+import * as fs from 'node:fs';
+import { assert, it } from 'vitest';
+import { parse, print } from 'svelte/compiler';
+import { try_load_json } from '../helpers.js';
+import { suite, type BaseTest } from '../suite.js';
+import { walk } from 'zimmerframe';
+import type { AST } from 'svelte/compiler';
+
+interface ParserTest extends BaseTest {}
+
+const { test, run } = suite<ParserTest>(async (config, cwd) => {
+	const input = fs.readFileSync(`${cwd}/input.svelte`, 'utf-8');
+
+	const ast = parse(input, { modern: true });
+	const output = print(ast);
+
+	// run `UPDATE_SNAPSHOTS=true pnpm test parser` to update parser tests
+	if (process.env.UPDATE_SNAPSHOTS) {
+		fs.writeFileSync(`${cwd}/output.svelte`, output.code);
+	} else {
+		fs.writeFileSync(`${cwd}/_actual.svelte`, output.code);
+
+		const file = `${cwd}/output.svelte`;
+
+		const expected = fs.existsSync(file) ? fs.readFileSync(file, 'utf-8') : '';
+		assert.deepEqual(output.code, expected);
+	}
+});
+
+export { test };
+
+await run(__dirname);