test: restore and fix unit tests

tests/unit/App.spec.js

@@ -0,0 +1,31 @@
+import { shallowMount, createLocalVue } from '@vue/test-utils'
+import VueRouter from 'vue-router'
+import CoreuiVue from '@coreui/vue'
+import App from '@/App'
+
+const localVue = createLocalVue()
+localVue.use(VueRouter)
+const router = new VueRouter()
+
+
+localVue.use(CoreuiVue)
+
+describe('App.vue', () => {
+  it('has a name', () => {
+    expect(App.name).toMatch('app')
+  })
+  it('is Vue instance', () => {
+    const wrapper = shallowMount(App, {
+      localVue,
+      router
+    })
+    expect(wrapper.isVueInstance()).toBe(true)
+  })
+  it('is App', () => {
+    const wrapper = shallowMount(App, {
+      localVue,
+      router
+    })
+    expect(wrapper.is(App)).toBe(true)
+  })
+})