Snapshot testing in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the snapshot testing utility from Vue Test Utils.

Vue

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

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

AshallowMount

Bmount

Crender

DcreateSnapshot

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'shallowMount' instead of 'mount' will not render child components fully.

Trying to import a non-existent function like 'createSnapshot'.

The mount function is used to render the component for snapshot testing.

2fill in blank

medium

Complete the code to create a snapshot test for the HelloWorld component.

Vue

test('renders correctly', () => {
  const wrapper = mount(HelloWorld);
  expect(wrapper.[1]()).toMatchSnapshot();
});

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

Ahtml

Btext

Celement

Drender

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'text()' will not capture the full HTML structure.

Using 'render()' is not a method on the wrapper.

The html() method returns the rendered HTML string for snapshot comparison.

3fill in blank

hard

Fix the error in the snapshot test by completing the missing method call.

Vue

const wrapper = mount(MyComponent);
expect(wrapper.[1]()).toMatchSnapshot();

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

Atext

Brender

Chtml

Dsnapshot

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'text()' instead of 'html()' causes incomplete snapshot data.

Trying to call a non-existent 'snapshot()' method.

The html() method returns the component's HTML for snapshot matching.

4fill in blank

hard

Fill both blanks to create a snapshot test that mounts the component and matches its HTML output.

Vue

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

test('snapshot test', () => {
  const wrapper = [2](MyComponent);
  expect(wrapper.html()).toMatchSnapshot();
});

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

Amount

BshallowMount

Crender

DcreateSnapshot

Attempts:

3 left

💡 Hint

Common Mistakes

Using different functions for import and mounting causes errors.

Using 'shallowMount' results in incomplete snapshots.

Use mount to fully render the component for snapshot testing.

5fill in blank

hard

Fill all three blanks to write a snapshot test that imports mount, mounts the component, and asserts the snapshot.

Vue

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

const wrapper = [2](MyComponent);

expect(wrapper.[3]()).toMatchSnapshot();

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

Amount

BshallowMount

Chtml

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'shallowMount' instead of 'mount' for full rendering.

Using 'text()' instead of 'html()' for snapshot content.

Import and use mount to render the component, then call html() to get the HTML for snapshot matching.

Practice

1. What is the main purpose of snapshot testing in Vue component testing?

easy

A. To test the component's methods and computed properties

B. To save the component's rendered HTML and detect unexpected UI changes

C. To check the component's CSS styles for correctness

D. To verify the component's event handlers are called

Solution

1. Step 1: Understand snapshot testing purpose

   Snapshot testing captures the rendered HTML output of a component to detect changes over time.

2. Step 2: Compare with other testing types

   Unlike method or event testing, snapshot testing focuses on UI structure, not behavior or styles.

3. Final Answer:

   To save the component's rendered HTML and detect unexpected UI changes -> Option B

4. Quick Check:

   Snapshot testing = UI output check [OK]

Hint: Snapshot testing checks UI output changes visually [OK]

Common Mistakes:

• Confusing snapshot testing with unit testing methods
• Thinking it tests CSS or events directly
• Assuming it tests component logic

2. Which of the following is the correct way to write a snapshot test for a Vue component using @vue/test-utils?

easy

A. expect(mount(MyComponent).html()).toMatchSnapshot()

B. expect(shallowMount(MyComponent).text()).toMatchSnapshot()

C. expect(mount(MyComponent).vm).toMatchSnapshot()

D. expect(renderToString(MyComponent)).toBeSnapshot()

Solution

1. Step 1: Identify correct mounting and snapshot method

   Using mount from @vue/test-utils and calling html() returns the rendered HTML string.

2. Step 2: Match snapshot with Jest matcher

   toMatchSnapshot() is the correct Jest matcher to compare the HTML output to the saved snapshot.

3. Final Answer:

   expect(mount(MyComponent).html()).toMatchSnapshot() -> Option A

4. Quick Check:

   mount + html() + toMatchSnapshot() = correct syntax [OK]

Hint: Use mount().html() with toMatchSnapshot() for Vue snapshots [OK]

Common Mistakes:

• Using shallowMount instead of mount when full HTML is needed
• Trying to snapshot the component instance (vm) instead of HTML
• Using incorrect matcher like toBeSnapshot()

3. Given this test code snippet, what will happen when the component's HTML changes unexpectedly?

import { mount } from '@vue/test-utils'
import MyComponent from './MyComponent.vue'
test('renders correctly', () => {
  const wrapper = mount(MyComponent)
  expect(wrapper.html()).toMatchSnapshot()
})

medium

A. The test will fail indicating the snapshot does not match the new HTML

B. The test will pass regardless of HTML changes

C. The test will throw a syntax error

D. The test will update the snapshot automatically

Solution

1. Step 1: Understand snapshot comparison behavior

   When the component's HTML changes, Jest compares the new output to the saved snapshot and detects differences.

2. Step 2: Result of mismatch

   If the HTML differs unexpectedly, the test fails to alert the developer about the change.

3. Final Answer:

   The test will fail indicating the snapshot does not match the new HTML -> Option A

4. Quick Check:

   Snapshot mismatch causes test failure [OK]

Hint: Snapshot test fails if UI output changes unexpectedly [OK]

Common Mistakes:

• Assuming tests auto-update snapshots without command
• Thinking test passes even if HTML changes
• Confusing syntax errors with snapshot failures

4. You wrote this snapshot test but it always fails with an error:

expect(wrapper.html().toMatchSnapshot())

What is the problem and how to fix it?

medium

A. toMatchSnapshot() is not a valid Jest matcher; fix by using toEqualSnapshot()

B. wrapper.html() returns undefined; fix by using wrapper.text() instead

C. Missing import of toMatchSnapshot from Jest; fix by importing it explicitly

D. toMatchSnapshot() should be called on expect(), not on the string; fix: expect(wrapper.html()).toMatchSnapshot()

Solution

1. Step 1: Identify incorrect method chaining

   The code calls toMatchSnapshot() on the string result of wrapper.html(), which is incorrect.

2. Step 2: Correct usage of Jest matcher

   The matcher toMatchSnapshot() must be called on the expect() wrapper, not on the string itself.

3. Final Answer:

   toMatchSnapshot() should be called on expect(), not on the string; fix: expect(wrapper.html()).toMatchSnapshot() -> Option D

4. Quick Check:

   Call matcher on expect() result [OK]

Hint: Call toMatchSnapshot() on expect(), not on string [OK]

Common Mistakes:

• Calling matcher on string instead of expect()
• Using wrong matcher name
• Assuming wrapper.html() returns undefined

5. You have a Vue component that conditionally renders a button based on a prop. You want to snapshot test both states (button shown and hidden). How should you write your tests to handle this correctly?

hard

A. Write a test that updates the snapshot manually after each prop change

B. Write one test mounting the component without props and snapshot it once

C. Write two separate tests, each mounting the component with different prop values, and snapshot each output

D. Write one test mounting the component with both prop values at once and snapshot the combined output

Solution

1. Step 1: Understand conditional rendering impact

   The component's output changes based on the prop, so each state has a different HTML structure.

2. Step 2: Write separate snapshot tests per state

   Mount the component twice with different prop values and snapshot each output separately to catch changes in both states.

3. Final Answer:

   Write two separate tests, each mounting the component with different prop values, and snapshot each output -> Option C

4. Quick Check:

   Separate snapshots for different states [OK]

Hint: Test each UI state separately with its own snapshot [OK]

Common Mistakes:

• Trying to snapshot multiple states in one test
• Not passing props to trigger conditional rendering
• Updating snapshots without verifying changes