chore: globally .use(Vuex) when using instantiated store (#247)

src/__tests__/vuex.js

@@ -1,5 +1,6 @@
 import '@testing-library/jest-dom'
 import {render, fireEvent} from '@testing-library/vue'
+import Vue from 'vue'
 import Vuex from 'vuex'
 
 import VuexTest from './components/Store/VuexTest'
@@ -57,6 +58,12 @@ test('can render with vuex with custom store', async () => {
 })
 
 test('can render with an instantiated Vuex store', async () => {
+  // Before calling new Vuex.Store in your code, you'll need to `.use` it on the
+  // global (or local) Vue instance. In frameworks like Jest, the `setupFilesAfterEnv`
+  // property is a good place to do this.
+  // https://jestjs.io/docs/configuration#setupfilesafterenv-array
+  Vue.use(Vuex)
+
   const {getByTestId, getByText} = render(VuexTest, {
     store: new Vuex.Store({
       state: {count: 3},