javascript - How to mock Firebase Firestore methods using Jest?

Javascript - How to mock Firebase Firestore methods using Jest?

Mocking Firebase Firestore methods using Jest in JavaScript involves creating mock implementations for Firestore functions to simulate behavior and responses during testing. Here's a step-by-step guide on how to mock Firestore methods for testing purposes:

1. Setup Jest and Firebase Mock

First, make sure you have Jest installed in your project. If not, install it using npm or yarn:

npm install --save-dev jest

Next, you'll need a way to mock Firebase Firestore. One popular library for this is firebase-mock, which provides a mock implementation of Firestore that you can use in your Jest tests. Install firebase-mock:

npm install --save-dev firebase-mock

2. Create a Mock Firestore Module

Create a mock Firestore module that exports mocked Firestore functions. This mock module will be used in place of the actual Firestore module during testing.

// mockFirestore.js

const { MockFirestore } = require('firebase-mock');

const mockFirestore = new MockFirestore();

module.exports = mockFirestore;

3. Configure Jest Setup File

Create a setup file for Jest (jest.setup.js or any name you prefer) to configure Jest before running tests. This file will set up mocks for Firebase Firestore.

// jest.setup.js

const mockFirestore = require('./mockFirestore');

jest.mock('firebase', () => ({
  initializeApp: jest.fn(),
  firestore: () => mockFirestore,
}));

4. Write Your Jest Test

Now, you can write your Jest test file (example.test.js) and use the mocked Firestore methods.

// example.test.js

const firebase = require('firebase');

test('should fetch data from Firestore', async () => {
  // Mock Firestore data
  const mockData = { id: '1', name: 'John Doe' };
  const mockSnapshot = { data: () => mockData };

  // Mock Firestore collection and document methods
  const collectionMock = jest.fn().mockReturnValue({
    doc: jest.fn().mockReturnValue({
      get: jest.fn().mockResolvedValue(mockSnapshot),
    }),
  });

  firebase.firestore = jest.fn().mockReturnValue({
    collection: collectionMock,
  });

  // Example test case
  const firestore = firebase.firestore();
  const doc = firestore.collection('users').doc('1');
  const snapshot = await doc.get();

  expect(snapshot.data()).toEqual(mockData);
});

Explanation:

  • Mock Setup (jest.setup.js): In this file, you mock firebase.initializeApp() and firebase.firestore() to return mockFirestore, which is the mocked Firestore instance created using firebase-mock.

  • Test File (example.test.js):

    • Mock Firestore methods (collection(), doc(), and get()) using jest.fn() to simulate Firestore queries and responses.
    • Use Jest's expect() to assert that the data fetched from Firestore matches the expected mock data.

Running Tests

Run your Jest tests using the Jest CLI:

jest --setupFiles ./jest.setup.js

This command tells Jest to use jest.setup.js as the setup file before running tests.

Notes:

  • Adjust the mock Firestore methods (collectionMock, docMock, etc.) in example.test.js according to your specific Firestore query requirements.
  • Firebase-mock may not support all Firebase Firestore functionalities. Ensure the mock implementation meets your testing needs.

By following these steps, you can effectively mock Firebase Firestore methods using Jest for unit testing your JavaScript code that interacts with Firestore operations. Adjust the setup and tests as necessary based on your project's requirements and Firestore usage.

Examples

  1. Jest mock Firestore collection get example

    Description: Learn how to mock Firestore's collection and get methods in Jest for testing Firebase interactions.

    // Mocking Firestore collection().get() in Jest
jest.mock('firebase/firestore', () => ({
    collection: jest.fn(() => ({
        get: jest.fn(() => Promise.resolve({ docs: [] })),
    })),
}));

// Example test
test('Firestore collection get test', async () => {
    const { collection } = require('firebase/firestore');
    const snapshot = await collection('testCollection').get();
    expect(snapshot.docs.length).toBe(0);
});

  2. Mock Firestore document get using Jest

    Description: Implement Jest mock for Firestore's doc and get methods to simulate fetching a document.

    // Mocking Firestore doc().get() in Jest
jest.mock('firebase/firestore', () => ({
    doc: jest.fn(() => ({
        get: jest.fn(() => Promise.resolve({ data: () => ({}) })),
    })),
}));

// Example test
test('Firestore document get test', async () => {
    const { doc } = require('firebase/firestore');
    const docSnapshot = await doc('testCollection/testDoc').get();
    expect(docSnapshot.data()).toEqual({});
});

  3. Jest mock Firestore query snapshot

    Description: Use Jest to mock Firestore's query and get methods to simulate querying and fetching multiple documents.

    // Mocking Firestore query().get() in Jest
jest.mock('firebase/firestore', () => ({
    query: jest.fn(() => ({
        get: jest.fn(() => Promise.resolve({ docs: [{ data: () => ({}) }] })),
    })),
}));

// Example test
test('Firestore query get test', async () => {
    const { query } = require('firebase/firestore');
    const querySnapshot = await query('testCollection').get();
    expect(querySnapshot.docs.length).toBe(1);
    expect(querySnapshot.docs[0].data()).toEqual({});
});

  4. Jest mock Firestore set method

    Description: Create a Jest mock for Firestore's set method to test document creation or updating.

    // Mocking Firestore doc().set() in Jest
jest.mock('firebase/firestore', () => ({
    doc: jest.fn(() => ({
        set: jest.fn(() => Promise.resolve()),
    })),
}));

// Example test
test('Firestore document set test', async () => {
    const { doc } = require('firebase/firestore');
    await doc('testCollection/testDoc').set({ key: 'value' });
    expect(doc().set).toHaveBeenCalledWith({ key: 'value' });
});

  5. Jest mock Firestore update method

    Description: Implement Jest mock for Firestore's update method to test document updates.

    // Mocking Firestore doc().update() in Jest
jest.mock('firebase/firestore', () => ({
    doc: jest.fn(() => ({
        update: jest.fn(() => Promise.resolve()),
    })),
}));

// Example test
test('Firestore document update test', async () => {
    const { doc } = require('firebase/firestore');
    await doc('testCollection/testDoc').update({ key: 'updatedValue' });
    expect(doc().update).toHaveBeenCalledWith({ key: 'updatedValue' });
});

  6. Mock Firestore delete method using Jest

    Description: Use Jest to mock Firestore's delete method for testing document deletion.

    // Mocking Firestore doc().delete() in Jest
jest.mock('firebase/firestore', () => ({
    doc: jest.fn(() => ({
        delete: jest.fn(() => Promise.resolve()),
    })),
}));

// Example test
test('Firestore document delete test', async () => {
    const { doc } = require('firebase/firestore');
    await doc('testCollection/testDoc').delete();
    expect(doc().delete).toHaveBeenCalled();
});

  7. Jest mock Firestore transaction

    Description: Create a Jest mock for Firestore's runTransaction method to simulate transactional operations.

    // Mocking Firestore runTransaction() in Jest
jest.mock('firebase/firestore', () => ({
    runTransaction: jest.fn((transactionFunc) => transactionFunc()),
}));

// Example test
test('Firestore transaction test', async () => {
    const { runTransaction } = require('firebase/firestore');
    const result = await runTransaction(async (transaction) => {
        // Perform transactional operations
        return 'transactionCompleted';
    });
    expect(result).toBe('transactionCompleted');
});

  8. Jest mock Firestore batch

    Description: Implement Jest mock for Firestore's batch method to test batched write operations.

    // Mocking Firestore batch() in Jest
jest.mock('firebase/firestore', () => ({
    batch: jest.fn(() => ({
        set: jest.fn(),
        update: jest.fn(),
        delete: jest.fn(),
        commit: jest.fn(() => Promise.resolve()),
    })),
}));

// Example test
test('Firestore batch test', async () => {
    const { batch } = require('firebase/firestore');
    const firestoreBatch = batch();
    firestoreBatch.set('testCollection/testDoc', { key: 'value' });
    await firestoreBatch.commit();
    expect(firestoreBatch.set).toHaveBeenCalledWith('testCollection/testDoc', { key: 'value' });
});

  9. Jest mock Firestore listener

    Description: Use Jest to mock Firestore's onSnapshot method for testing real-time listeners.

    // Mocking Firestore doc().onSnapshot() in Jest
jest.mock('firebase/firestore', () => ({
    doc: jest.fn(() => ({
        onSnapshot: jest.fn((callback) => callback({ data: () => ({}) })),
    })),
}));

// Example test
test('Firestore listener test', async () => {
    const { doc } = require('firebase/firestore');
    const unsubscribe = doc('testCollection/testDoc').onSnapshot(snapshot => {
        expect(snapshot.data()).toEqual({});
    });
    unsubscribe();
});

  10. Jest mock Firestore error handling

    Description: Implement Jest mock for Firestore methods with error handling to simulate error scenarios.

    // Mocking Firestore methods with error handling in Jest
jest.mock('firebase/firestore', () => ({
    doc: jest.fn(() => ({
        get: jest.fn(() => Promise.reject(new Error('Document not found'))),
        set: jest.fn(() => Promise.reject(new Error('Error setting document'))),
    })),
}));

// Example test
test('Firestore error handling test', async () => {
    const { doc } = require('firebase/firestore');
    
    // Testing get method error
    await expect(doc('testCollection/testDoc').get()).rejects.toThrow('Document not found');

    // Testing set method error
    await expect(doc('testCollection/testDoc').set({ key: 'value' })).rejects.toThrow('Error setting document');
});

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