chore: add testcases

Author: hackape

packages/svelte/test/runtime/samples/binding-backflow/Child.svelte

@@ -0,0 +1,21 @@
+<script>
+  export let testcase;
+	export let value = { foo: 'kid' };
+
+  if (testcase === 'init_update') {
+    value = { foo: 'kid' }
+  }
+
+  $: if (testcase === 'reactive_update') {
+    value = { foo: 'kid' }
+  }
+
+  $: if (testcase === 'reactive_mutate') {
+    value.foo = 'kid'
+  }
+
+	export let updates = [];
+	$: updates = [...updates, value];
+</script>
+
+<div>child: {value?.foo} | updates: {updates.length}</div>

packages/svelte/test/runtime/samples/binding-backflow/Parent.svelte

@@ -0,0 +1,12 @@
+<script>
+	import Child from './Child.svelte';
+	export let child;
+
+	export let testcase;
+	export let value;
+	export let updates = [];
+	$: updates = [...updates, value];
+</script>
+
+<div>parent: {value?.foo} | updates: {updates.length}</div>
+<Child bind:value bind:this={child} {testcase} />

packages/svelte/test/runtime/samples/binding-backflow/_config.js

@@ -0,0 +1,40 @@
+export default {
+	get props() {
+		return {
+			configs: [
+				{ testcase: 'parent_override_child_default', value: { foo: 'mon' } },
+				{ testcase: 'child_default_populate_parent', value: undefined },
+				{ testcase: 'reactive_update', value: { foo: 'mon' } },
+				{ testcase: 'reactive_mutate', value: { foo: 'mon' } },
+				{ testcase: 'init_update', value: { foo: 'mon' } }
+			]
+		};
+	},
+
+	async test({ assert, component }) {
+		const parents = component.parents;
+
+		// first testcase should update once
+		// the rest should update twice
+		let p;
+		p = parents['parent_override_child_default'];
+		assert.deepEqual(p.value, { foo: 'mon' });
+		assert.equal(p.updates.length, 1);
+
+		p = parents['child_default_populate_parent'];
+		assert.deepEqual(p.value, { foo: 'kid' });
+		assert.equal(p.updates.length, 2);
+
+		p = parents['reactive_update'];
+		assert.deepEqual(p.value, { foo: 'kid' });
+		assert.equal(p.updates.length, 2);
+
+		p = parents['reactive_mutate'];
+		assert.deepEqual(p.value, { foo: 'kid' });
+		assert.equal(p.updates.length, 2);
+
+		p = parents['init_update'];
+		assert.deepEqual(p.value, { foo: 'kid' });
+		assert.equal(p.updates.length, 2);
+	}
+};

packages/svelte/test/runtime/samples/binding-backflow/main.svelte

@@ -0,0 +1,9 @@
+<script>
+	import Parent from './Parent.svelte';
+	export let configs = [];
+	export let parents = {};
+</script>
+
+{#each configs as config}
+	<Parent bind:this={parents[config.testcase]} value={config.value} testcase={config.testcase} />
+{/each}