add test

packages/svelte/tests/compiler-errors/samples/snippet-invalid-export/_config.js

@@ -0,0 +1,10 @@
+import { test } from '../../test';
+
+export default test({
+	error: {
+		code: 'snippet_invalid_export',
+		message:
+			'An exported snippet can only reference things declared in a `<script module>`, or other exportable snippets',
+		position: [26, 29]
+	}
+});

packages/svelte/tests/compiler-errors/samples/snippet-invalid-export/main.svelte

@@ -0,0 +1,11 @@
+<script module>
+	export { foo }
+</script>
+
+<script>
+	let x = 42;
+</script>
+
+{#snippet foo()}
+	{x}
+{/snippet}