add basic unit test for expandable navgroup component

__tests__/components/NavExpandableGroup.test.jsx

@@ -0,0 +1,29 @@
+import React from 'react';
+import { MemoryRouter } from 'react-router-dom';
+import { mount } from 'enzyme';
+
+import { Nav } from '@patternfly/react-core';
+import NavExpandableGroup from '../../src/components/NavExpandableGroup';
+
+describe('NavExpandableGroup', () => {
+  test('initialization and render', () => {
+    const component = mount(
+      <MemoryRouter initialEntries={['/foo']}>
+        <Nav aria-label="Test Navigation">
+          <NavExpandableGroup
+            groupId="test"
+            title="Test"
+            routes={[
+              { path: '/foo', title: 'Foo' },
+              { path: '/bar', title: 'Bar' },
+              { path: '/fiz', title: 'Fiz' },
+            ]}
+          />
+        </Nav>
+      </MemoryRouter>
+    ).find('NavExpandableGroup').instance();
+
+    expect(component.navItemPaths).toEqual(['/foo', '/bar', '/fiz']);
+    expect(component.isActiveGroup()).toEqual(true);
+  });
+});