Mastering Vue 3 Testing with Custom Jest Presets

Testing Vue 3 applications is crucial for ensuring robust and maintainable code. While Jest provides excellent testing capabilities, setting up reusable configurations and utilities for your Vue components can become repetitive. This challenge focuses on creating a custom Jest preset to streamline your Vue 3 testing environment.

Problem Description

Your task is to create a custom Jest preset for testing Vue 3 components written in TypeScript. This preset should:

• Configure Jest for Vue 3 and TypeScript: Ensure Jest can correctly process .vue files and TypeScript code without manual per-project configuration.
• Provide common testing utilities: Include helpful utilities for mounting Vue components, such as mount from @vue/test-utils and potentially pre-configured mocks or stubs.
• Simplify test setup: Allow developers to simply specify your preset in their jest.config.js to get a fully functional Vue 3 testing environment.

You'll need to define the structure of your preset, how it will be referenced, and what it will export to achieve this goal.

Examples

Example 1: Basic Usage

Consider a simple Vue component MyButton.vue:

<template>
  <button @click="$emit('click')">{{ label }}</button>
</template>

<script lang="ts">
import { defineComponent } from 'vue';

export default defineComponent({
  props: {
    label: {
      type: String,
      required: true,
    },
  },
  emits: ['click'],
});
</script>

And a test file MyButton.spec.ts:

import { mount, VueWrapper } from '@vue/test-utils';
import MyButton from './MyButton.vue';

describe('MyButton', () => {
  it('renders the correct label and emits click event', async () => {
    const wrapper: VueWrapper<any> = mount(MyButton, {
      props: { label: 'Click Me' },
    });

    expect(wrapper.text()).toBe('Click Me');

    await wrapper.find('button').trigger('click');
    expect(wrapper.emitted('click')).toHaveLength(1);
  });
});

With your custom Jest preset applied, the jest.config.js file in the project would look like:

// jest.config.js
module.exports = {
  preset: 'your-custom-vue-jest-preset', // This line applies your preset
  // Other project-specific configurations can go here
};

The test should pass without any further Jest configuration in the project.

Example 2: Integration with TypeScript

Consider a more complex component UserProfile.vue that uses TypeScript features:

<template>
  <div>
    <h2>{{ user.name }}</h2>
    <p>Email: {{ user.email }}</p>
  </div>
</template>

<script lang="ts">
import { defineComponent, PropType } from 'vue';

interface User {
  id: number;
  name: string;
  email: string;
}

export default defineComponent({
  props: {
    user: {
      type: Object as PropType<User>,
      required: true,
    },
  },
});
</script>

And its test UserProfile.spec.ts:

import { mount, VueWrapper } from '@vue/test-utils';
import UserProfile from './UserProfile.vue';

describe('UserProfile', () => {
  it('displays user information correctly', () => {
    const mockUser = {
      id: 1,
      name: 'Jane Doe',
      email: 'jane.doe@example.com',
    };
    const wrapper: VueWrapper<any> = mount(UserProfile, {
      props: { user: mockUser },
    });

    expect(wrapper.find('h2').text()).toBe('Jane Doe');
    expect(wrapper.find('p').text()).toBe('Email: jane.doe@example.com');
  });
});

Your preset should ensure that PropType and other TypeScript features within the Vue component's script block are correctly handled by Jest.

Constraints

• The preset must be installable via npm/yarn and usable with the preset option in jest.config.js.
• The preset should be compatible with Vue 3 and Jest v27+.
• The preset should support TypeScript out of the box.
• The primary goal is to reduce boilerplate for Vue 3 + TypeScript projects. You are not required to implement complex mocking or stubbing, but your preset should provide the foundational setup.

Notes

• Consider using babel-jest or ts-jest for transpiling TypeScript and @vue/vue3-jest for handling .vue files.
• Think about what essential modules you might want to expose or make easily accessible within your preset's setup.
• The output of your preset will be a Jest configuration object. You might need to export functions that Jest calls to resolve this configuration.
• The challenge is to create the preset, not to use it in a larger project (though thinking about usage helps in design). You should demonstrate how your preset would be structured.