Add more unit tests and update integration tests

tests/unit/404Page.spec.js

@@ -0,0 +1,20 @@
+import { expect } from 'chai'
+import { shallowMount, RouterLinkStub } from '@vue/test-utils'
+import page404 from '@/pages/404Page.vue'
+
+describe('404Page.vue Component Test', () => {
+  let wrapper;
+  beforeEach(() => {
+    wrapper = shallowMount(page404, {
+      global: {
+        stubs: {
+          'router-link': RouterLinkStub
+        }
+      }
+    })
+  })
+
+  it('Mount test', () => {
+    expect(wrapper.text()).to.include('404');
+  })
+})