How to test Vue watcher that watches a computed property from VueX?

Question

Suppose I have the following component:

import { mapState } from \'vuex\';
import externalDependency from \'...\';

export default {
  name: \'Foo\',
  computed:         


        

Answer 1

The Vue Test Utils documentation points at a different approach where you use a very simple Vuex store:

import { shallowMount, createLocalVue } from '@vue/test-utils'
import Vuex from 'vuex'

// use a localVue to prevent vuex state from polluting the global Vue instance
const localVue = createLocalVue();
localVue.use(Vuex);

describe('Foo.vue', () => {
  let state;
  let store;

  beforeEach(() => {
    // create a new store for each test to prevent pollution
    state = { bar: 'bar' };
    store = new Vuex.Store({ state });
  })

  it('should call externalDependency.doThing with bar', () => 
  {
    shallowMount(MyComponent, { store, localVue });
    const spy = jest.spyOn(externalDependency, 'doThing');
    // trigger the watch
    state.bar = 'baz';
    expect(spy).toHaveBeenCalledWith('baz');
  });
})