Vitest setup in Svelte - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Vitest test function.

Svelte

import { [1] } from 'vitest';

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

Atest

Brun

Ccheck

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong import name like 'run' or 'check'.

Forgetting to import the test function.

The test function is imported from Vitest to define test cases.

2fill in blank

medium

Complete the code to assert that a value is true using Vitest.

Svelte

import { test, expect } from 'vitest';
test('check true', () => {
  expect(true).[1]();
});

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

AtoBeFalse

BtoEqualTrue

CtoEqualFalse

DtoBeTruthy

Attempts:

3 left

💡 Hint

Common Mistakes

Using toEqualTrue() which is not a Vitest matcher.

Using toBeFalse() by mistake.

The toBeTruthy() matcher checks if the value is truthy.

3fill in blank

hard

Fix the error in the Vitest config import statement.

Svelte

import { defineConfig } from '[1]';

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

Asvelte

Bvite

Cvitest/config

Dvitest

Attempts:

3 left

💡 Hint

Common Mistakes

Importing defineConfig from vitest or vite causes errors.

Using svelte as import source here.

The Vitest config helper defineConfig is imported from vitest/config.

4fill in blank

hard

Fill both blanks to create a Vitest config with Svelte plugin.

Svelte

import { defineConfig } from 'vitest/config';
import [1] from '@sveltejs/vite-plugin-svelte';

export default defineConfig({
  plugins: [[2]()] 
});

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

Asvelte

Bvitest

CsveltePlugin

Dvite

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for import and usage causes errors.

Importing from wrong packages.

The Svelte plugin is imported as svelte and used as svelte() in plugins.

5fill in blank

hard

Fill all three blanks to write a basic Vitest test for a Svelte component.

Svelte

import { test, expect } from 'vitest';
import [1] from './MyComponent.svelte';
import { render } from '@testing-library/svelte';

test('renders component', () => {
  const { [2] } = render([3]);
  expect(container).toBeTruthy();
});

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

AMyComponent

Bcontainer

Drender

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names for destructuring.

Passing wrong argument to render function.

We import the component as MyComponent, destructure container from render(MyComponent), then check if container exists.

Practice

1. What is the main purpose of Vitest in a Svelte project?

easy

A. To deploy the app to a server

B. To build the Svelte app for production

C. To style components with CSS

D. To run tests and check if components work correctly

Solution

1. Step 1: Understand Vitest's role

   Vitest is a testing tool used to verify code correctness.

2. Step 2: Compare options with Vitest's purpose

   Only To run tests and check if components work correctly describes testing, which matches Vitest's function.

3. Final Answer:

   To run tests and check if components work correctly -> Option D

4. Quick Check:

   Vitest = Testing tool [OK]

Hint: Vitest is for testing, not building or styling [OK]

Common Mistakes:

• Confusing Vitest with build tools
• Thinking Vitest styles components
• Assuming Vitest deploys apps

2. Which of the following is the correct way to configure Vitest for Svelte testing in vite.config.js?

easy

A. import { defineConfig } from 'vite'; export default defineConfig({ plugins: [], test: { environment: 'node' } });

B. import { defineConfig } from 'vite'; import svelte from '@sveltejs/vite-plugin-svelte'; export default defineConfig({ plugins: [], test: { environment: 'jsdom' } });

C. import { defineConfig } from 'vite'; import svelte from '@sveltejs/vite-plugin-svelte'; export default defineConfig({ plugins: [svelte()], test: { environment: 'jsdom' } });

D. import { defineConfig } from 'vitest'; import svelte from '@sveltejs/vite-plugin-svelte'; export default defineConfig({ plugins: [svelte()] });

Solution

1. Step 1: Check plugin usage for Svelte

   The Svelte plugin must be included in plugins array for Svelte support.

2. Step 2: Verify test environment setting

   Vitest tests for Svelte need 'jsdom' environment to simulate browser.

3. Final Answer:

   Correct config includes Svelte plugin and jsdom environment -> Option C

4. Quick Check:

   Plugin + jsdom = Correct Vitest config [OK]

Hint: Include svelte plugin and set environment to jsdom [OK]

Common Mistakes:

• Omitting the Svelte plugin
• Using 'node' instead of 'jsdom' environment
• Importing defineConfig from wrong package

3. Given this test code for a Svelte component using Vitest and @testing-library/svelte:

import { render } from '@testing-library/svelte';
import Button from './Button.svelte';

test('shows button text', () => {
  const { getByText } = render(Button, { props: { label: 'Click me' } });
  getByText('Click me');
});

What happens if the component does NOT display the label prop text?

medium

A. The test throws a syntax error

B. The test fails with an error that text was not found

C. The test passes silently

D. The test logs a warning but passes

Solution

1. Step 1: Understand getByText behavior

   getByText throws an error if the text is not found in the rendered output.

2. Step 2: Analyze test outcome if label missing

   If the component does not show 'Click me', getByText fails and test fails.

3. Final Answer:

   The test fails with an error that text was not found -> Option B

4. Quick Check:

   getByText missing text = test fail [OK]

Hint: getByText throws error if text missing, causing test failure [OK]

Common Mistakes:

• Assuming test passes without text
• Confusing runtime errors with syntax errors
• Thinking warnings allow test to pass

4. You wrote this Vitest config snippet:

import { defineConfig } from 'vite';
import svelte from '@sveltejs/vite-plugin-svelte';

export default defineConfig({
  plugins: [svelte()],
  test: {
    environment: 'node'
  }
});

Why might your Svelte component tests fail to run correctly?

medium

A. Because the test environment is set to 'node' instead of 'jsdom'

B. Because the Svelte plugin is missing from plugins

C. Because defineConfig must be imported from 'vitest' not 'vite'

D. Because the test property should be outside defineConfig

Solution

1. Step 1: Check environment setting for browser features

   Svelte components need a browser-like environment; 'node' lacks DOM APIs.

2. Step 2: Understand impact on tests

   Using 'node' causes tests that rely on DOM (like rendering) to fail.

3. Final Answer:

   Because the test environment is set to 'node' instead of 'jsdom' -> Option A

4. Quick Check:

   Use jsdom for DOM tests, not node [OK]

Hint: Use 'jsdom' environment for Svelte component tests [OK]

Common Mistakes:

• Thinking 'node' environment supports DOM
• Confusing import source for defineConfig
• Misplacing test config outside defineConfig

5. You want to test a Svelte component that conditionally renders a message only if a prop show is true. Which Vitest test code correctly checks that the message appears only when show is true?

import { render } from '@testing-library/svelte';
import Message from './Message.svelte';

test('message visibility', () => {
  // Fill in test code here
});

hard

A. const { queryByText } = render(Message, { props: { show: false } });
expect(queryByText('Hello')).toBeNull();
const { getByText } = render(Message, { props: { show: true } });
getByText('Hello');

B. const { getByText } = render(Message, { props: { show: false } });
getByText('Hello');

C. const { getByText } = render(Message, { props: { show: true } });
expect(getByText('Hello')).toBeNull();

D. const { queryByText } = render(Message, { props: { show: true } });
expect(queryByText('Hello')).toBeNull();

Solution

1. Step 1: Test absence when show is false

   Use queryByText to check 'Hello' is not rendered (returns null).

2. Step 2: Test presence when show is true

   Use getByText to confirm 'Hello' is rendered and found.

3. Final Answer:

   Use queryByText for absence and getByText for presence in two renders -> Option A

4. Quick Check:

   queryByText null means no text; getByText finds text [OK]

Hint: Use queryByText to check absence, getByText to check presence [OK]

Common Mistakes:

• Using getByText expecting null when text missing
• Not testing both true and false cases
• Confusing queryByText and getByText roles