tests: add test that exposes sveltejs#3634

test/runtime/samples/reactive-compound-operator/_config.js

@@ -0,0 +1,29 @@
+export default {
+	skip_if_ssr: true, // TODO delete this line, once binding works
+
+	html: `
+		<button>+1</button>
+		<p>count: 0</p>
+	`,
+
+	async test({ assert, component, target, window }) {
+		const click = new window.MouseEvent('click');
+		const button = target.querySelector('button');
+
+		await button.dispatchEvent(click);
+
+		assert.equal(component.x, 2);
+		assert.htmlEqual(target.innerHTML, `
+			<button>+1</button>
+			<p>count: 2</p>
+		`);
+
+		await button.dispatchEvent(click);
+
+		assert.equal(component.x, 6);
+		assert.htmlEqual(target.innerHTML, `
+			<button>+1</button>
+			<p>count: 6</p>
+		`);
+	}
+};

test/runtime/samples/reactive-compound-operator/main.svelte

@@ -0,0 +1,9 @@
+<script>
+	export let x = 0;
+
+    $: x *= 2;
+
+</script>
+
+<button on:click='{() => x += 1}'>+1</button>
+<p>count: {x}</p>