Mocking composables and stores in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the composable correctly.

Vue

import { [1] } from '@/composables/useUser';

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

AuseUser

BUserStore

CgetUser

DuseStore

Attempts:

3 left

💡 Hint

Common Mistakes

Using the store name instead of the composable name.

Forgetting the curly braces around the import.

The composable is named useUser and should be imported with that exact name.

2fill in blank

medium

Complete the code to mock the store using Pinia's testing utilities.

Vue

import { createTestingPinia } from '@pinia/testing';

const pinia = createTestingPinia({
  [1]: false
});

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

AdisableActions

BmockActions

CstubActions

DfakeActions

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect option names like 'mockActions' which do not exist.

Confusing the option with disabling the entire store.

The option stubActions controls whether actions are stubbed or not in the testing Pinia instance.

3fill in blank

hard

Fix the error in mocking a composable by completing the jest.mock statement.

Vue

jest.mock('@/composables/useUser', () => ({
  [1]: () => ({ name: 'Test User' })
}));

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

AgetUser

BuseUser

CuserStore

DmockUser

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different function name that does not match the composable.

Forgetting to return an object from the mocked function.

The mocked function must match the composable name useUser to replace it correctly.

4fill in blank

hard

Fill both blanks to mock a Pinia store and override a getter.

Vue

import { setActivePinia, createPinia } from 'pinia';

setActivePinia(createPinia());
const store = useUserStore();
store.[1] = [2];

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

Aname

B'Mock User'

CuserName

D'Test User'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong property name like 'userName' which does not exist.

Assigning a variable instead of a string literal.

The store property name is overridden with the string 'Test User' to mock the getter value.

5fill in blank

hard

Fill all three blanks to mock a composable and test its returned value.

Vue

import { mount } from '@vue/test-utils';
import Component from '@/components/UserProfile.vue';

jest.mock('@/composables/useUser', () => ({
  [1]: () => ({
    name: '[2]'
  })
}));

const wrapper = mount(Component);
expect(wrapper.text()).toContain('[3]');

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

AuseUser

BMock User

DgetUser

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different composable name in the mock.

Mismatching the mocked name and the expected text in the test.

The composable useUser is mocked to return a name 'Mock User'. The test checks that the component renders this name.

Practice

1. What is the main reason to mock composables or stores in Vue component tests?

easy

A. To automatically generate UI snapshots

B. To improve the component's runtime performance

C. To isolate the component test from real logic and external dependencies

D. To enable two-way data binding in tests

Solution

1. Step 1: Understand the purpose of mocking

   Mocking replaces real implementations with fake ones to isolate tests from external logic.

2. Step 2: Apply this to composables and stores

   Mocking composables and stores prevents side effects and focuses tests on the component itself.

3. Final Answer:

   To isolate the component test from real logic and external dependencies -> Option C

4. Quick Check:

   Mocking isolates tests = A [OK]

Hint: Mock to isolate component logic from external code [OK]

Common Mistakes:

• Thinking mocking improves runtime performance
• Confusing mocking with UI snapshot generation
• Believing mocking enables data binding

2. Which syntax correctly mocks a composable module named useAuth using Vitest's vi.mock()?

easy

A. vi.mock('./useAuth', () => ({ useAuth: () => ({ isLoggedIn: true }) }))

B. vi.mock('useAuth', () => ({ isLoggedIn: true }))

C. vi.mock('useAuth', () => ({ useAuth: () => ({ isLoggedIn: true }) }))

D. vi.mock('./useAuth', () => ({ isLoggedIn: true }))

Solution

1. Step 1: Identify the module path

   Modules are mocked by their relative or absolute path, so './useAuth' is correct if the file is local.

2. Step 2: Provide a factory returning the mocked composable function

   The factory must return an object with the composable function that returns the mocked state.

3. Final Answer:

   vi.mock('./useAuth', () => ({ useAuth: () => ({ isLoggedIn: true }) })) -> Option A

4. Quick Check:

   Correct path and factory function = C [OK]

Hint: Mock with correct path and return a function for composables [OK]

Common Mistakes:

• Using module name without path when path is required
• Returning state object directly instead of a function
• Mocking without a factory function

3. Given this mocked store code snippet:

vi.mock('./store', () => ({ useStore: () => ({ count: 5, increment: vi.fn() }) }))

const store = useStore();
store.increment();
console.log(store.count);

What will be logged to the console?

medium

A. undefined

B. 5

C. Error: increment is not a function

D. 0

Solution

1. Step 1: Analyze the mocked store return values

   The mocked useStore returns an object with count: 5 and increment as a mock function.

2. Step 2: Check the console.log output

   The count property is 5 and is not changed by calling increment() because it's a mock function without implementation.

3. Final Answer:

   5 -> Option B

4. Quick Check:

   Mocked count value logged = 5 [OK]

Hint: Mocked state stays same unless mock function changes it [OK]

Common Mistakes:

• Assuming mock function changes state automatically
• Expecting undefined because increment is mocked
• Confusing mock function with real implementation

4. Identify the error in this test mocking a composable:

vi.mock('./useCounter', () => ({
  useCounter: {
    count: 0,
    increment: vi.fn()
  }
}))

medium

A. The mock should return a function, not an object directly

B. The vi.fn() should be replaced with a real function

C. The module path './useCounter' is incorrect

D. The mock should not include the increment function

Solution

1. Step 1: Understand composable mocking pattern

   Composable modules export functions, so mocks must return a function, not an object.

2. Step 2: Identify the incorrect mock structure

   The code returns an object directly instead of a function returning the object.

3. Final Answer:

   The mock should return a function, not an object directly -> Option A

4. Quick Check:

   Composable mocks return functions = D [OK]

Hint: Mock composables as functions returning objects [OK]

Common Mistakes:

• Returning object directly instead of function
• Replacing vi.fn() unnecessarily
• Incorrect module path assumptions

5. You want to test a Vue component that uses a Pinia store with a fetchData action. How do you mock the store to verify fetchData is called without running its real logic?

hard

A. Replace fetchData with an empty async function in the real store

B. Import the real store and spy on fetchData without mocking

C. Mock the component instead of the store

D. Use vi.mock() to replace the store module with a mock where fetchData is a vi.fn()

Solution

1. Step 1: Understand mocking for store actions

   To isolate tests, replace the store module with a mock that has fetchData as a mock function.

2. Step 2: Use vi.mock() to replace the store module

   This allows you to track calls to fetchData without executing its real code.

3. Final Answer:

   Use vi.mock() to replace the store module with a mock where fetchData is a vi.fn() -> Option D

4. Quick Check:

   Mock store action with vi.fn() = A [OK]

Hint: Mock store actions with vi.fn() to track calls without side effects [OK]

Common Mistakes:

• Not mocking the store and calling real logic
• Mocking the component instead of the store
• Replacing functions with empty but untracked implementations