add test

Author: Rich-Harris

packages/svelte/tests/runtime-runes/samples/effect-root-5/_config.js

@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs }) {
+		const [b1, b2] = target.querySelectorAll('button');
+
+		flushSync(() => b1.click());
+		assert.deepEqual(logs, [0, 1]);
+
+		flushSync(() => b1.click());
+		assert.deepEqual(logs, [0, 1, 2]);
+
+		flushSync(() => b2.click());
+		assert.deepEqual(logs, [0, 1, 2]);
+	}
+});

packages/svelte/tests/runtime-runes/samples/effect-root-5/main.svelte

@@ -0,0 +1,23 @@
+<script>
+	let obj = $state({ count: 0 });
+
+	$effect.root(() => {
+		let teardown;
+
+		$effect.pre(() => {
+			if (obj) {
+				teardown ??= $effect.root(() => {
+					$effect.pre(() => {
+						console.log(obj.count);
+					});
+				});
+			} else {
+				teardown?.();
+				teardown = null;
+			}
+		});
+	});
+</script>
+
+<button onclick={() => ((obj ??= { count: 0 }).count += 1)}>+1</button>
+<button onclick={() => (obj = null)}>null</button>