add test

test/runtime/samples/event-handler-modifier-body-once/_config.js

@@ -0,0 +1,11 @@
+export default {
+	async test({ assert, component, window }) {
+		const event = new window.MouseEvent('click');
+
+		await window.document.body.dispatchEvent(event);
+		assert.equal(component.count, 1);
+
+		await window.document.body.dispatchEvent(event);
+		assert.equal(component.count, 1);
+	}
+};

test/runtime/samples/event-handler-modifier-body-once/main.svelte

@@ -0,0 +1,5 @@
+<script>
+	export let count = 0;
+</script>
+
+<svelte:body on:click|once="{() => count += 1}"/>