Component testing with Vue Test Utils - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the mount function from Vue Test Utils.

Vue

import { [1] } from '@vue/test-utils';

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

AshallowMount

Brender

CcreateApp

Dmount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'render' instead of 'mount' will cause errors.

Using 'createApp' is for app initialization, not testing.

The mount function is used to create a wrapper for the component in tests.

2fill in blank

medium

Complete the code to mount the HelloWorld component in the test.

Vue

const wrapper = [1](HelloWorld);

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

Amount

BcreateApp

Crender

DshallowMount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'render' will not create a wrapper object.

Using 'shallowMount' renders without child components.

Use mount to fully render the component for testing.

3fill in blank

hard

Fix the error in the test assertion to check the component text content.

Vue

expect(wrapper.text()).toBe([1]);

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

A'Hello World!'

B`Hello World!`

C"Hello World!"

DHello World!

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes causes syntax errors.

Using backticks is valid but not the expected answer here.

The expected value must be a string literal, so it needs quotes.

4fill in blank

hard

Fill both blanks to find a button and trigger a click event in the test.

Vue

const button = wrapper.find([1]);
await button.[2]('click');

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

A"button"

Bclick

Ctrigger

D"#submit"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'click()' directly on the wrapper is incorrect.

Not quoting the selector causes errors.

Use find("button") to select the button element and trigger('click') to simulate the click event.

5fill in blank

hard

Fill all three blanks to create a test that mounts a component, triggers a click, and checks emitted events.

Vue

const wrapper = [1](MyButton);
await wrapper.find('button').[2]('click');
expect(wrapper.emitted()).toHaveProperty([3]);

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

Amount

Btrigger

C'click'

DshallowMount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'shallowMount' instead of 'mount' changes test behavior.

Forgetting quotes around event name causes errors.

This test mounts the component, triggers a click event, and checks if the 'click' event was emitted.

Practice

1. What is the primary purpose of using mount() from Vue Test Utils in component testing?

easy

A. To compile Vue components into production code

B. To deploy Vue components to a server

C. To style Vue components with CSS

D. To create a full instance of a Vue component for testing its behavior

Solution

1. Step 1: Understand the role of mount()

   mount() creates a real instance of a Vue component in a test environment.

2. Step 2: Identify what mount() is NOT for

   It is not used for compiling, styling, or deploying components.

3. Final Answer:

   To create a full instance of a Vue component for testing its behavior -> Option D

4. Quick Check:

   mount() creates component instance [OK]

Hint: Remember: mount() means create component instance [OK]

Common Mistakes:

• Confusing mount() with build or deploy tools
• Thinking mount() styles components
• Assuming mount() compiles code

2. Which of the following is the correct way to import mount from Vue Test Utils in a test file?

easy

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

B. import mount from 'vue-test-utils';

C. const mount = require('vue-test-utils');

D. import { mount } from 'vue';

Solution

1. Step 1: Check the official import syntax

   The correct import uses named import from '@vue/test-utils'.

2. Step 2: Identify incorrect import styles

   import mount from 'vue-test-utils'; uses default import incorrectly, C uses CommonJS require which is outdated here, A imports from wrong package.

3. Final Answer:

   import { mount } from '@vue/test-utils'; -> Option A

4. Quick Check:

   Correct import syntax = import { mount } from '@vue/test-utils'; [OK]

Hint: Use named import from '@vue/test-utils' [OK]

Common Mistakes:

• Using default import instead of named import
• Using require() instead of import
• Importing from wrong package

3. Given this test code snippet:

const wrapper = mount({ template: '{{ count }}', data() { return { count: 0 } } });
await wrapper.find('button').trigger('click');
console.log(wrapper.text());

What will be logged to the console?

medium

A. 0

B. click

C. 1

D. undefined

Solution

1. Step 1: Understand the component behavior

   The button shows the current count, starting at 0, and increments count on click.

2. Step 2: Analyze the test actions

   The test triggers a click event on the button, increasing count from 0 to 1, then logs the button text.

3. Final Answer:

   1 -> Option C

4. Quick Check:

   Click increments count, text shows 1 [OK]

Hint: Click triggers count++ so text updates to 1 [OK]

Common Mistakes:

• Assuming text stays 0 after click
• Confusing event name with text output
• Forgetting to await trigger for update

4. What is wrong with this test code snippet?

const wrapper = mount(MyComponent);
wrapper.find('button').trigger('click');
expect(wrapper.text()).toContain('Clicked');

medium

A. Missing await before trigger to wait for DOM update

B. Incorrect selector used in find()

C. Missing import of mount from Vue Test Utils

D. Using expect() incorrectly without a matcher

Solution

1. Step 1: Identify asynchronous DOM update

   Triggering events may update DOM asynchronously, so awaiting trigger is needed.

2. Step 2: Check the code for await usage

   The code calls trigger() without await, so the expect() runs before DOM updates.

3. Final Answer:

   Missing await before trigger to wait for DOM update -> Option A

4. Quick Check:

   Await trigger() for DOM update [OK]

Hint: Always await trigger() to ensure DOM updates before assertions [OK]

Common Mistakes:

• Not awaiting trigger causing test to fail
• Assuming find() selector is wrong without checking
• Forgetting to import mount (not shown here)
• Misusing expect() matcher syntax

5. You want to test a component that emits a custom event submit with a payload object when a form is submitted. Which Vue Test Utils method correctly checks the event and its payload?

hard

A. expect(wrapper.find('form').trigger('submit')).toBeTruthy();

B. expect(wrapper.emitted().submit[0]).toEqual([{ name: 'John' }]);

C. expect(wrapper.text()).toContain('submit');

D. expect(wrapper.props().submit).toBeDefined();

Solution

1. Step 1: Understand event emission checking

   Vue Test Utils stores emitted events in wrapper.emitted(), accessible by event name and call index.

2. Step 2: Verify correct assertion for event payload

   expect(wrapper.emitted().submit[0]).toEqual([{ name: 'John' }]); checks the first submit event payload matches the expected object, which is correct.

3. Final Answer:

   expect(wrapper.emitted().submit[0]).toEqual([{ name: 'John' }]); -> Option B

4. Quick Check:

   Use emitted() to check event and payload [OK]

Hint: Use wrapper.emitted() to check events and payloads [OK]

Common Mistakes:

• Checking text instead of emitted events
• Testing props instead of events
• Not accessing emitted event payload array