tests: runtime: add test to trap invalid dynamic event values

test/runtime/samples/event-handler-dynamic-invalid/_config.js

@@ -0,0 +1,28 @@
+export default {
+	html: `<button>undef</button>
+	<button>null</button>
+	<button>invalid</button>`,
+
+	async test({ assert, component, target, window }) {
+		const [buttonUndef, buttonNull, buttonInvalid] = target.querySelectorAll(
+			'button'
+		);
+
+		const event = new window.MouseEvent('click');
+		let err = "";
+		window.addEventListener('error', (e) => {
+			e.preventDefault();
+			err = e.message;
+		});
+
+		// All three should not throw if proper checking is done in runtime code
+		await buttonUndef.dispatchEvent(event);
+		assert.equal(err, "", err);
+
+		await buttonNull.dispatchEvent(event);
+		assert.equal(err, "", err);
+
+		await buttonInvalid.dispatchEvent(event);
+		assert.equal(err, "", err);
+	},
+};

test/runtime/samples/event-handler-dynamic-invalid/main.svelte

@@ -0,0 +1,13 @@
+<script>
+	let handlerUndef;
+	let handlerNull;
+	let handlerInvalid;
+
+	handlerUndef = undefined;
+	handlerNull = null;
+	handlerInvalid = 42;
+</script>
+
+<button on:click={handlerUndef}>undef</button>
+<button on:click={handlerNull}>null</button>
+<button on:click={handlerInvalid}>invalid</button>