[improvement] test utils ts (#3024)

test/demo-test.ts

@@ -0,0 +1,22 @@
+import Vue from 'vue';
+import '../docs/src/demo-common';
+import Locale from '../packages/locale';
+import { renderToString } from '@vue/server-test-utils';
+
+const empty = {
+  template: '<div><slot></slot></div>',
+  inheritAttrs: false
+};
+
+Vue.component('demo-block', empty);
+Vue.component('demo-section', empty);
+
+export default function (Demo: any) {
+  test('renders demo correctly', () => {
+    if (Demo.i18n) {
+      Locale.add(Demo.i18n);
+    }
+
+    expect(renderToString(Demo)).toMatchSnapshot();
+  });
+}