feat: add test for onDestroy call with transition nested component(sveltejs#5268)

Author: seo-rii

test/runtime/samples/transition-js-outro/Inner.svelte

@@ -0,0 +1,8 @@
+<script>
+	import { onDestroy, createEventDispatcher } from 'svelte';
+	const dispatch = createEventDispatcher();
+
+	onDestroy(() => dispatch('destroyed'));
+</script>
+
+<div></div>

test/runtime/samples/transition-js-outro/_config.js

@@ -0,0 +1,8 @@
+export default {
+	test({ assert, component, raf }) {
+		component.visible = false;
+
+		raf.tick(50);
+		assert.equal(component.destroyed, true);
+	}
+};

test/runtime/samples/transition-js-outro/main.svelte

@@ -0,0 +1,24 @@
+<script>
+	import Inner from './Inner.svelte';
+
+	export let visible = true, destroyed = false;
+
+	function foo(node) {
+		return {
+			duration: 100,
+			tick: t => {
+				node.foo = t;
+			}
+		};
+	}
+
+	const onDestroy = () => {
+		destroyed = true;
+	};
+</script>
+
+{#if visible}
+	<div transition:foo>
+		<Inner on:destroyed={onDestroy}/>
+	</div>
+{/if}