How to Mock postgresql (pg) in node.js using jest

Question

I am new in node.js. I am writing code in node.js for postgresql using pg and pg-native for serverless app. I need to write unit test for it. I am unable to mock pg client using jest or sinon.

My actual code is like this

const { Client } = require('pg');
export const getAlerts = async (event, context) => {

  const client = new Client({
    user: process.env.DB_USER,
    host: process.env.DB_HOST,
    database: process.env.DB_DATABASE,
    password: process.env.DB_PASSWORD,
    port: process.env.PORT
  });

  await client.connect();

  try {
    const result = await client.query(`SELECT * FROM public.alerts;`);
    console.log(result.rows);
    client.end();
    return success({ message: `${result.rowCount} item(s) returned`, data: result.rows, status: true });

  } catch (e) {
    console.error(e.stack);
    client.end();
    return failure({ message: e, status: false });
  }

};

How to mock pg client here?

Answer 1

Here is the unit test solution using jestjs:

index.js:

const { Client } = require('pg');
const { success, failure } = require('./handler');

export const getAlerts = async (event, context) => {
  const client = new Client({
    user: process.env.DB_USER,
    host: process.env.DB_HOST,
    database: process.env.DB_DATABASE,
    password: process.env.DB_PASSWORD,
    port: process.env.PORT,
  });

  await client.connect();

  try {
    const result = await client.query(`SELECT * FROM public.alerts;`);
    console.log(result.rows);
    client.end();
    return success({ message: `${result.rowCount} item(s) returned`, data: result.rows, status: true });
  } catch (e) {
    console.error(e.stack);
    client.end();
    return failure({ message: e, status: false });
  }
};

hander.js:

export function success(data) {}
export function failure(data) {}

index.spec.js:

import { getAlerts } from './';
import { Client } from 'pg';
import { success, failure } from './handler';

jest.mock('pg', () => {
  const mClient = {
    connect: jest.fn(),
    query: jest.fn(),
    end: jest.fn(),
  };
  return { Client: jest.fn(() => mClient) };
});

jest.mock('./handler.js', () => {
  return {
    success: jest.fn(),
    failure: jest.fn(),
  };
});

describe('59540432', () => {
  let client;
  beforeEach(() => {
    client = new Client();
  });
  afterEach(() => {
    jest.clearAllMocks();
  });
  it('should success', async () => {
    client.query.mockResolvedValueOnce({ rows: [], rowCount: 0 });
    await getAlerts();
    expect(client.connect).toBeCalledTimes(1);
    expect(client.query).toBeCalledWith('SELECT * FROM public.alerts;');
    expect(client.end).toBeCalledTimes(1);
    expect(success).toBeCalledWith({ message: '0 item(s) returned', data: [], status: true });
  });

  it('should failure', async () => {
    const mError = new Error('dead lock');
    client.query.mockRejectedValueOnce(mError);
    await getAlerts();
    expect(client.connect).toBeCalledTimes(1);
    expect(client.query).toBeCalledWith('SELECT * FROM public.alerts;');
    expect(client.end).toBeCalledTimes(1);
    expect(failure).toBeCalledWith({ message: mError, status: false });
  });
});

Unit test result with 100% coverage:

 PASS  src/stackoverflow/59540432/index.spec.js (11.792s)
  59540432
    ✓ should success (16ms)
    ✓ should failure (5ms)

  console.log src/stackoverflow/59540432/index.js:3131
    []

  console.error src/stackoverflow/59540432/index.js:3155
    Error: dead lock
        at /Users/ldu020/workspace/github.com/mrdulin/jest-codelab/src/stackoverflow/59540432/index.spec.js:39:20
        at step (/Users/ldu020/workspace/github.com/mrdulin/jest-codelab/src/stackoverflow/59540432/index.spec.js:33:23)
        at Object.next (/Users/ldu020/workspace/github.com/mrdulin/jest-codelab/src/stackoverflow/59540432/index.spec.js:14:53)
        at /Users/ldu020/workspace/github.com/mrdulin/jest-codelab/src/stackoverflow/59540432/index.spec.js:8:71
        at new Promise (<anonymous>)
        at Object.<anonymous>.__awaiter (/Users/ldu020/workspace/github.com/mrdulin/jest-codelab/src/stackoverflow/59540432/index.spec.js:4:12)
        at Object.<anonymous> (/Users/ldu020/workspace/github.com/mrdulin/jest-codelab/src/stackoverflow/59540432/index.spec.js:38:24)
        at Object.asyncJestTest (/Users/ldu020/workspace/github.com/mrdulin/jest-codelab/node_modules/jest-jasmine2/build/jasmineAsyncInstall.js:102:37)
        at resolve (/Users/ldu020/workspace/github.com/mrdulin/jest-codelab/node_modules/jest-jasmine2/build/queueRunner.js:43:12)
        at new Promise (<anonymous>)
        at mapper (/Users/ldu020/workspace/github.com/mrdulin/jest-codelab/node_modules/jest-jasmine2/build/queueRunner.js:26:19)
        at promise.then (/Users/ldu020/workspace/github.com/mrdulin/jest-codelab/node_modules/jest-jasmine2/build/queueRunner.js:73:41)
        at process._tickCallback (internal/process/next_tick.js:68:7)

----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |      100 |      100 |      100 |      100 |                   |
 index.js |      100 |      100 |      100 |      100 |                   |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        14.109s

Source code: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/59540432

Answer 2

Its an old question, but here is a new answer:

You can have a look at pg-mem, a library I released recently which emulates an in-memory postgres instance.

It supports most of the usual SQL queries (but will fail on less frequent syntaxes - file an issue if you encounter such a situation).

I wrote an article about it here

For your use case (how to use it with pg), see the this wiki section