add a test for #8459

test/runtime/samples/await-no-extra-unmount/Component.svelte

@@ -0,0 +1,7 @@
+<script>
+	import { onMount } from 'svelte';
+	export let mounts;
+	onMount(() => { ++mounts });
+</script>
+
+This component has been mounted {mounts} times.

test/runtime/samples/await-no-extra-unmount/_config.js

@@ -0,0 +1,6 @@
+export default {
+	async test({ assert, target }) {
+		await new Promise(f => setTimeout(f, 0));
+		assert.htmlEqual(target.innerHTML, 'This component has been mounted 1 times.');
+	}
+};

test/runtime/samples/await-no-extra-unmount/main.svelte

@@ -0,0 +1,14 @@
+<script>
+	import Component from "./Component.svelte";
+	let mounts = 0;
+	let promise = Promise.resolve();
+
+	(async () => {
+		await Promise.resolve();
+		promise = Promise.resolve();
+	})();
+</script>
+
+{#await promise then _}
+	<Component bind:mounts />
+{/await}