feat: add fail test

test/runtime/samples/inline-style-become-undefined/_config.js

@@ -0,0 +1,11 @@
+export default {
+	async test({ assert, target, window }) {
+		const div = target.querySelector('div');
+		const click = new window.MouseEvent('click');
+
+		assert.htmlEqual(target.innerHTML, '<div style="background: red;"></div>');
+		await div.dispatchEvent(click);
+		await Promise.resolve();
+		assert.htmlEqual(target.innerHTML, '<div style=""></div>');
+	}
+};

test/runtime/samples/inline-style-become-undefined/main.svelte

@@ -0,0 +1,9 @@
+<script>
+	let bg = "red";
+
+	const handle = () => {
+			bg = undefined;
+	};
+</script>
+
+<div style:background={bg} on:click={handle}></div>