add test, changeset

.changeset/brave-baboons-teach.md

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+---
+'svelte': minor
+---
+
+feat: async fragments

packages/svelte/tests/runtime-runes/samples/async-const/_config.js

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+import { test } from '../../test';
+
+export default test({
+	html: `<h1>Loading...</h1>`,
+
+	async test({ assert, target }) {
+		await new Promise((resolve) => setTimeout(resolve, 100));
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+            <h1>Hello, world!</h1>
+            <input type="text"/>
+			`
+		);
+	}
+});

packages/svelte/tests/runtime-runes/samples/async-const/main.svelte

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+<script>
+    let name = $state('world');
+    /**
+     * @template T
+     * @param {T} value
+     * @param {number} ms
+     * @returns {Promise<T>}
+     */
+    function wait(value, ms) {
+        return new Promise(resolve => setTimeout(resolve, ms, value));
+    }
+</script>
+<svelte:boundary>
+    {#snippet pending()}
+        <h1>Loading...</h1>
+    {/snippet}
+    {#snippet greet()}
+        {@const greeting = await wait(`Hello, ${name}!`, 50)}
+        <h1>{greeting}</h1>
+        <input type="text" bind:value={name} />
+    {/snippet}
+    {@render greet()}
+</svelte:boundary>