test: add missing snapshot tests to split-layout (#9945)

Author: web-padawan

packages/split-layout/test/dom/__snapshots__/split-layout.test.snap.js

@@ -0,0 +1,31 @@
+/* @web/test-runner snapshot v1 */
+export const snapshots = {};
+
+snapshots["vaadin-split-layout host"] = 
+`<vaadin-split-layout orientation="horizontal">
+</vaadin-split-layout>
+`;
+/* end snapshot vaadin-split-layout host */
+
+snapshots["vaadin-split-layout shadow"] = 
+`<slot
+  id="primary"
+  name="primary"
+>
+</slot>
+<div
+  id="splitter"
+  part="splitter"
+  style="touch-action: none;"
+>
+  <div part="handle">
+  </div>
+</div>
+<slot
+  id="secondary"
+  name="secondary"
+>
+</slot>
+`;
+/* end snapshot vaadin-split-layout shadow */
+

packages/split-layout/test/dom/split-layout.test.js

@@ -0,0 +1,20 @@
+import { expect } from '@vaadin/chai-plugins';
+import { fixtureSync, nextRender } from '@vaadin/testing-helpers';
+import '../../src/vaadin-split-layout.js';
+
+describe('vaadin-split-layout', () => {
+  let layout;
+
+  beforeEach(async () => {
+    layout = fixtureSync('<vaadin-split-layout></vaadin-split-layout>');
+    await nextRender();
+  });
+
+  it('host', async () => {
+    await expect(layout).dom.to.equalSnapshot();
+  });
+
+  it('shadow', async () => {
+    await expect(layout).shadowDom.to.equalSnapshot();
+  });
+});