Testing Component Methods in Vue.js using jest

In this tutorial, we are going to learn about how to test vue.js component methods using jest and vue-test-utils.

In vue methods help us to add functionalities to vue components.

If you don’t know how to configure jest with vue you can check out my previous tutorial.

The example component we are testing now.

Welcome.vue
<template>
  <div>
    <h1>{{title}}</h1>    <button @click="changeTitle">Change title</button>  </div>
</template>

<script>
export default {
  data: function() {
    return {
      title: "Hello"    };
  },
  methods: {
    changeTitle() {
      this.title = "Hi";    }
  }
};
</script>

In the above component, we have defined a changeTitle method which is used to update the title property.

Let’s write tests for the Welcome component changeTitle method.

The vue-test-utils wrapper object provides us a component instance via vm property by using that we can call component methods and also access data properties.

Welcome.test.js
import { shallowMount } from '@vue/test-utils';
import Post from '../src/components/Welcome.vue'
describe('Testing Component Methods', () => {
    const wrapper = shallowMount(Post);

    it('correctly updates the title when changeTitle is called', () => {

        expect(wrapper.vm.title).toBe('Hello'); //initial title Hello        wrapper.vm.changeTitle();  // calling component method        expect(wrapper.vm.title).toBe('Hi'); // title updates to Hi
    })

})

In the above code, we are testing for the component data property title to be Hi when a changeTitle() method is called.