test(CellGroup): update test cases

src/cell-group/test/__snapshots__/index.spec.js.snap

@@ -0,0 +1,8 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`should render title slot and match snapshot 1`] = `
+<div class="van-cell-group__title">Custom Title</div>
+<div class="van-cell-group van-hairline--top-bottom">
+  <!---->
+</div>
+`;

src/cell-group/test/index.spec.js

@@ -0,0 +1,12 @@
+import CellGroup from '..';
+import { mount } from '@vue/test-utils';
+
+test('should render title slot and match snapshot', () => {
+  const wrapper = mount(CellGroup, {
+    slots: {
+      title: () => 'Custom Title',
+    },
+  });
+
+  expect(wrapper.html()).toMatchSnapshot();
+});