Why testing Vue apps matters - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple test that checks if a Vue component renders correctly.

Vue

import { mount } from '@vue/test-utils'
import HelloWorld from './HelloWorld.vue'

test('renders message', () => {
  const wrapper = mount(HelloWorld)
  expect(wrapper.text()).toContain([1])
})

Drag options to blanks, or click blank then click option'

A"Hello World"

BHello World

C'Hello World'

DHelloWorld

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the string

Using component name instead of text

We use a string with quotes to check if the rendered text contains 'Hello World'.

2fill in blank

medium

Complete the code to simulate a button click in a Vue test.

Vue

const wrapper = mount(ButtonComponent)
await wrapper.find('button').[1]
expect(wrapper.emitted()).toHaveProperty('click')

Drag options to blanks, or click blank then click option'

Aclick

Btrigger('click')

Cemit

Dfire

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'click()' directly

Using 'emit' instead of 'trigger'

We use trigger to simulate DOM events like clicks in Vue tests.

3fill in blank

hard

Fix the error in the test by completing the code to wait for Vue's DOM updates.

Vue

import { nextTick } from 'vue'

const wrapper = mount(Component)
wrapper.setData({ count: 1 })
await [1]()
expect(wrapper.text()).toContain('1')

Drag options to blanks, or click blank then click option'

AnextTick

BsetTimeout

CflushPromises

Dtick

Attempts:

3 left

💡 Hint

Common Mistakes

Using setTimeout instead of nextTick

Not waiting for DOM updates

Vue's nextTick waits for DOM updates after data changes.

4fill in blank

hard

Fill both blanks to create a computed property and use it in the template.

Vue

<template>
  <p>{{ [1] }}</p>
</template>

<script setup>
import { computed, ref } from 'vue'
const count = ref(0)
const [2] = computed(() => count.value * 2)
</script>

Drag options to blanks, or click blank then click option'

AdoubleCount

Bcount

Ccount * 2

Ddouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names in template and script

Using expressions directly in template

The computed property is named doubleCount and used in the template with the same name.

5fill in blank

hard

Fill all three blanks to create a reactive state, update it, and check the rendered output.

Vue

<template>
  <button @click="[1]">Increment</button>
  <p>{{ count }}</p>
</template>

<script setup>
import { ref } from 'vue'
const count = ref(0)
function [2]() {
  count.value [3] 1
}
</script>

Drag options to blanks, or click blank then click option'

Aincrement

BincrementCount

C+=

D++

Attempts:

3 left

💡 Hint

Common Mistakes

Using different function names

Using ++ on ref directly

The button calls the increment function which increases count.value by 1 using +=.

Practice

1. Why is testing Vue apps important before releasing them to users?

easy

A. It helps find bugs early to avoid problems for users

B. It makes the app load faster

C. It changes the app's design automatically

D. It reduces the app's file size

Solution

1. Step 1: Understand the purpose of testing

   Testing is done to catch errors and bugs before users see them.

2. Step 2: Compare options with testing goals

   Only It helps find bugs early to avoid problems for users matches the goal of finding bugs early to improve user experience.

3. Final Answer:

   It helps find bugs early to avoid problems for users -> Option A

4. Quick Check:

   Testing finds bugs early = C [OK]

Hint: Testing finds bugs before users do [OK]

Common Mistakes:

• Thinking testing improves app speed
• Believing testing changes design automatically
• Confusing testing with file size reduction

2. Which of the following is the correct way to write a simple test in Vue using Jest?

easy

A. test('renders message') => { expect(wrapper.text()).toContain('Hello') }

B. test 'renders message' { expect(wrapper.text()).toContain('Hello') }

C. test('renders message', () => { expect(wrapper.text()).toContain('Hello') })

D. test('renders message', () => expect(wrapper.text()).contains('Hello'))

Solution

1. Step 1: Review Jest test syntax

   Jest tests use the format test('name', () => { ... }) with expect inside.

2. Step 2: Identify correct syntax

   test('renders message', () => { expect(wrapper.text()).toContain('Hello') }) matches correct Jest syntax with arrow function and expect().toContain().

3. Final Answer:

   test('renders message', () => { expect(wrapper.text()).toContain('Hello') }) -> Option C

4. Quick Check:

   Correct Jest test syntax = A [OK]

Hint: Jest tests use test('name', () => { ... }) [OK]

Common Mistakes:

• Omitting arrow function parentheses
• Using wrong expect matcher like contains
• Missing commas or braces in test function

3. Given this Vue test snippet, what will be the output if the component renders 'Welcome' text?

const wrapper = mount(MyComponent)
expect(wrapper.text()).toContain('Welcome')

medium

A. Test passes because 'Welcome' is found

B. Test fails because 'Welcome' is missing

C. Syntax error in test code

D. Runtime error due to missing mount function

Solution

1. Step 1: Understand what wrapper.text() does

   It returns the text content of the mounted component.

2. Step 2: Check if 'Welcome' is in the text

   The component renders 'Welcome', so expect(wrapper.text()).toContain('Welcome') passes.

3. Final Answer:

   Test passes because 'Welcome' is found -> Option A

4. Quick Check:

   Text contains 'Welcome' = Test passes [OK]

Hint: If text matches, expect().toContain() passes [OK]

Common Mistakes:

• Assuming test fails if text is present
• Confusing syntax errors with runtime errors
• Forgetting to mount component before testing

4. Identify the error in this Vue test code:

const wrapper = mount(MyComponent)
expect(wrapper.text()).toContain('Hello')
expect(wrapper.find('button').click()).toBe(true)

medium

A. No error, code is correct

B. Missing import for mount function

C. Incorrect expect matcher for text content

D. Using click() inside expect without triggering event properly

Solution

1. Step 1: Review how to trigger events in Vue tests

   click() is a method that triggers the event but does not return true/false.

2. Step 2: Check usage inside expect()

   Using expect(wrapper.find('button').click()).toBe(true) is wrong because click() returns undefined.

3. Final Answer:

   Using click() inside expect without triggering event properly -> Option D

4. Quick Check:

   click() returns undefined, not true [OK]

Hint: click() triggers event; don't expect its return value [OK]

Common Mistakes:

• Expecting click() to return true
• Not importing mount from test utils
• Using wrong matcher for text content

5. You want to ensure your Vue app remains reliable as you add features. Which testing approach helps catch future bugs early and saves time?

hard

A. Test only the UI design without functionality checks

B. Write automated unit and integration tests for components

C. Skip testing and fix bugs when users report them

D. Only test manually after all features are done

Solution

1. Step 1: Understand testing approaches

   Automated unit and integration tests check small parts and their interactions early.

2. Step 2: Compare options for reliability and time saving

   Write automated unit and integration tests for components helps catch bugs early and saves time by preventing future errors.

3. Final Answer:

   Write automated unit and integration tests for components -> Option B

4. Quick Check:

   Automated tests catch bugs early = D [OK]

Hint: Automated tests catch bugs early and save time [OK]

Common Mistakes:

• Relying only on manual testing after development
• Ignoring tests until users find bugs
• Testing only UI without functionality