How to test Vuex Mutations using Vue-test-utils and Jest

Question

I have checked at least a couple of tutorials on mocking and testing Vuex actions but I wasn't able to successfully implement them on my own. It would always result having toHaveBeenCalled to false though I followed most of the steps provided on the links above. You can mock Actions without having to replicate their actual functionality using jest.fn() right? I don't get why I still can't successfully pull this off.

store.js

export default new Vuex.Store({
  state: {
    currentSequence: ''
  },
  actions: {
    runGenerator({ commit, state }, currentSequence) {
      // do something with currentSequence
    }
  }
})

Home.vue (Take note that this not the entire code for this component but I listed the important ones including the submit.prevent method, the html that contains the form and where the vuex action is called)

<template>
  <v-app id="inspire">
    <v-form @submit.prevent="setNextVal" id="sequence-form">
      <!-- form contents here -->
    </v-form>
  </v-app>
</template>

<script>
import { mapActions } from 'vuex'

export default {
  methods: {
    setNextVal() {
      this.runGenerator(this.form.currentSequence)
      this.form.currentValue = this.getCurrentValue
    },
    ...mapActions([
      'runGenerator'
    ]),
  }
}
</script>

store.spec.js

import { shallowMount, createLocalVue } from '@vue/test-utils'
import Vue from 'vue'
import Vuex from 'vuex'
import Vuetify from 'vuetify'
import Home from '@/views/Home.vue'

const localVue = createLocalVue()

localVue.use(Vuex)
Vue.use(Vuetify)

describe('Home.vue', () => {

  let actions
  let store

  beforeEach(() => {
    actions = {
      runGenerator: jest.fn()
    }
    store = new Vuex.Store({
      state: {
        currentSequence: ''
      },
      actions
    })
  })

  it('Dispatches "runGenerator" when submit.prevent has been triggered', () => {
    const wrapper = shallowMount(Home, { store, localVue })
    const form = wrapper.find('#sequence-form')
    form.trigger('submit.prevent')

    expect(actions.runGenerator).toHaveBeenCalled()
  })
})

After running the test I get the following error:

expect(jest.fn()).toHaveBeenCalled() Expected mock function to have been called, but it was not called

What did I miss?? Please enlighten me guys.. I kept reading the reference provided online and I can't seem to find some other solutions online.

Answer 1

Even though you're mocking the actions, they're still technically asynchronous. When testing vuex, I always await async actions with flushPromises (which ensures any active promises are resolved before continuing execution). To add flushPromises to your project do the following:

npm i -D flush-promises

Then in your test:

import flushPromises from 'flush-promises'

//...

it('Dispatches "runGenerator" when submit.prevent has been triggered', async() => {
    const wrapper = shallowMount(Home, { store, localVue })
    const form = wrapper.find('#sequence-form')
    form.trigger('submit.prevent')

    await flushPromises();    

    expect(actions.runGenerator).toHaveBeenCalled()
})

Note that the test function is now labeled as async-