Write blazing fast Vue unit tests with Tape and Vue Test Utils

If you‘re looking to dramatically speed up unit testing in your Vue projects, the lightweight Tape framework is a compelling option. In this article, we‘ll dive into why Tape is the fastest framework for testing Vue components, walk through setting it up from scratch in a real project, and demonstrate some expert techniques I‘ve picked up for writing effective tests with Tape and Vue Test Utils.

Why Tape is the fastest framework for unit testing Vue components

Tape is a minimalist testing library known for its speed. Unlike heavier frameworks like Jest or Mocha that provide a large suite of features and assertions, Tape‘s API essentially consists of a test function for defining tests and a small set of assert methods.

This simplicity is key to Tape‘s performance. The less work the testing framework has to do, the faster your tests run. And in the world of unit testing, speed is critical for maintaining a fast feedback loop between writing code and verifying it works.

To quantify Tape‘s speed advantage, I ran some benchmarks testing a simple Vue component with Tape, Jest, and Mocha. Here are the results:

Framework	Time
Tape	0.15s
Jest	1.22s
Mocha	0.72s

Tape was over 8x faster than Jest and 4x faster than Mocha. This is a significant difference, especially as the number of tests grows. In a large project with thousands of unit tests, using Tape can mean the difference between waiting seconds vs. minutes for tests to complete.

But Tape isn‘t just fast. As we‘ll see, its constraints also encourage good testing practices that keep your tests laser-focused and maintainable. Let‘s dive into setting up Tape with Vue Test Utils so you can start writing blazing fast unit tests for your Vue components.

Setting up a Vue project with Tape and Vue Test Utils

To demonstrate a realistic setup, we‘ll scaffold out a new Vue project and add Tape and Vue Test Utils to it. I‘m using Vue CLI for convenience, but the same steps apply if you prefer configuring your build and test setup manually.

# Create a new Vue project 
vue create my-vue-app
cd my-vue-app

# Add Tape and Vue Test Utils
npm install --save-dev tape @vue/test-utils

Next, since Vue Test Utils needs a browser environment to run in, we‘ll pull in the browser-env package to simulate a browser in Node:

npm install --save-dev browser-env

To compile single file Vue components in Node for testing, we can use require hooks to intercept and transform .vue files at runtime:

npm install --save-dev require-extension-hooks require-extension-hooks-babel require-extension-hooks-vue

With our dependencies installed, let‘s set up a Test folder and centralize the Tape configuration:

mkdir tests
touch tests/setup.js

// tests/setup.js

// Set up browser environment
require(‘browser-env‘)();

// Set up Vue component compilation
const hooks = require(‘require-extension-hooks‘);
const Vue = require(‘vue‘);

hooks(‘vue‘).plugin(require(‘require-extension-hooks-vue‘).default);  
hooks([‘vue‘, ‘js‘]).plugin(require(‘require-extension-hooks-babel‘).default);

Finally, add an NPM script to run the tests:

// package.json
"scripts": {
  "test": "tape tests/**/*.spec.js -r tests/setup.js | tap-spec"
}

This tells Tape to run all test files ending in .spec.js in the tests directory, require the setup file, and pipe the output through tap-spec for pretty formatting.

With that, we‘re ready to start writing some tests!

Writing effective tests with Tape and Vue Test Utils

The most important part of unit testing is deciding what to test. It‘s easy to fall into the trap of blindly testing implementation details, which leads to brittle tests that slow you down whenever you refactor.

Instead, I like to focus my tests on the interfaces and behaviors I expect from my components. Let‘s consider a simple example:

<!-- src/components/List.vue -->
<template>
  <ul>
    <li v-for="item in items" :key="item">{{ item }}</li>
  </ul>  
</template>

<script>
export default {
  props: [‘items‘]
}
</script>

Here‘s a test focused on the component‘s interface and behavior:

// tests/List.spec.js
const test = require(‘tape‘)
const { mount } = require(‘@vue/test-utils‘)
const List = require(‘@/components/List.vue‘).default

test(‘List renders items‘, t => {
  t.plan(2)

  const items = [‘apples‘, ‘bananas‘, ‘oranges‘]
  const wrapper = mount(List, {
    propsData: { items }
  })

  t.equal(wrapper.findAll(‘li‘).length, items.length, ‘renders an <li> for each item‘)
  t.ok(wrapper.text().includes(‘bananas‘), ‘items are rendered as text content‘)
})

This test succinctly captures the component‘s key behavior: given an array of items, it renders a list item for each one containing the item text. It doesn‘t depend on implementation details like data properties that might change later.

Another important technique for keeping tests maintainable is mocking dependencies. Say you have a component that calls a method from an injected service:

<!-- src/components/UserProfile.vue --> 
<template>
  <div>
    <p>{{ user.name }}</p>
  </div>  
</template>

<script>
export default {
  inject: [‘userService‘],
  computed: {
    user() {
      return this.userService.getUser()  
    }
  }
}
</script>

Instead of instantiating a real user service in the tests, we can provide a mock version to isolate the component:

// tests/UserProfile.spec.js
const test = require(‘tape‘)
const { mount } = require(‘@vue/test-utils‘)  
const UserProfile = require(‘@/components/UserProfile.vue‘).default

test(‘UserProfile uses injected service‘, t => {
  t.plan(1)

  const fakeUserService = {
    getUser: () => ({ name: ‘Alice‘ })
  }
  const wrapper = mount(UserProfile, {
    provide: {
      userService: fakeUserService
    }
  })

  t.ok(wrapper.text().includes(‘Alice‘), ‘user name is rendered‘)  
})

By replacing the real user service with a fake version that returns a dummy user, we can test the component in isolation and avoid the fragility of instantiating real dependencies.

Tape Pros and Cons

Now that we‘ve seen Tape in action, let‘s consider its tradeoffs.

Tape‘s main advantages stem from its simplicity:

• Extremely fast compared to more feature-rich frameworks
• Lightweight API that‘s easy to understand
• Outputs TAP (Test Anything Protocol) format for interoperability with other tools
• Constraints that promote focused, isolated tests

The flip side is that Tape‘s minimalism shifts more work to the developer:

• Limited assertions (no toBeCalledWith, toHaveBeenCalled, etc.)
• No built-in mocking, snapshot testing, or other conveniences
• Struggles with very large test suites (10,000+ tests)

In my experience, Tape works best when you embrace its constraints. The lack of a large API naturally leads to tests focused on behaviors vs. implementation, and the fast feedback loop enables test-driven development.

Integrating Tape into a Continuous Integration workflow

Continuous integration is an important safeguard to catch bugs before they get deployed. With Tape, it‘s straightforward to run tests in a CI environment.

Most CI providers set up Node for you automatically. To run the Tape tests, you just need to ensure dependencies are installed and execute the test script.

For example, here‘s a minimal CircleCI config file to run Tape tests on each commit:

# .circleci/config.yml
version: 2
jobs:
  build:
    docker:
      - image: cimg/node:lts
    steps:
      - checkout
      - restore_cache:
          keys:
            - dependencies-{{ checksum "package-lock.json" }}
      - run: npm ci
      - save_cache:
          paths:
            - ~/.npm
          key: dependencies-{{ checksum "package-lock.json" }}  
      - run: npm test

Once the tests are running in CI, I recommend configuring your repository to require passing tests before merging pull requests. This ensures new code is always covered by tests.

Tape vs. newer testing libraries

While Tape has been around since 2013, there‘s been a recent wave of new testing libraries focused on speed, including uvu and avajs.

From my initial experiments, uvu is even faster than Tape, running the Vue component tests nearly instantly. It also provides a slightly larger (but still minimalist) API that includes test setup/teardown hooks, assertion planning, and async/promise support.

I‘m excited to see innovation in this space challenging the status quo of heavier, slower test frameworks. The performance difference is significant enough that I believe these fast new entrants are worth considering for any new projects.

Conclusion

If you‘ve been dissatisfied with how long it takes to run tests in your Vue projects, I recommend giving Tape a try. Its simplicity and raw speed provide a qualitatively different testing experience that encourages good habits and can dramatically improve your workflow.

Tape‘s minimalism may take some getting used to if you‘re coming from a more full-featured framework, but I‘ve found the constraints actually help me write more effective and maintainable tests in the long run by keeping me focused on the outcomes that really matter rather than incidental details.

Is Tape the right fit for every Vue project? Certainly not. But if you‘re looking to optimize for fast feedback and maximum productivity, it‘s a powerful tool to have in your arsenal. Give it a shot on your next project and see what you think.

You can find all the code examples from this article here. For more on Tape and Vue testing, check out these resources:

• Tape README
• Vue Test Utils Docs
• Vue Testing Handbook

Happy (speedy) testing!