Mock @slack/web-api for jest

Usage no npm install needed!

<script type="module">
  import slackWrenchJestMockWebClient from 'https://cdn.skypack.dev/@slack-wrench/jest-mock-web-client';


Jest Mock Slack Web Client

This package contains a type-safe mock of @slack/web-api. @slack-wrench/jest-mock-web-client allows you to easily mock your calls to Slack's api and allows you to return a fake response. This means you get all the power of jest.fn() with maintainable and predictable test cases.

Table of Contents


yarn add --dev @slack-wrench/jest-mock-web-client
# or
npm install --save-dev @slack-wrench/jest-mock-web-client


This mock is intended to be used as a manual mock.

Create a file for the web-api manual mock (__mocks__/@slack/web-api.js)

// __mocks__/@slack/web-api.js
const mockWebApi = require('@slack-wrench/jest-mock-web-client');

module.exports = mockWebApi(jest);

Test your code how you would expect:

// src/bot.spec.js
const { WebClient } = require('@slack/web-api');
const Bot = require('./bot');

describe('The Bot', () => {
  let bot;
  let client;

  beforeEach(() => {
    // Reset mocks for each test
    // In this example, bot creates a `new WebClient()`
    bot = new Bot();
    client = WebClient.mock.instances[0];

  it('Can say things', async () => {
    const message = 'Mocking Slack is easy!';
    // With the mock setup, this won't actually call to Slack's servers
    await bot.say(message);

        text: message,

Getting the mocked client

Mocked instances are exposed as jest automatic mocks. You can find created instances at WebClient.mock.instances.

Mocking responses

By default, all methods resolve with { ok: true }. If you want to change that, every function is a jest mock function so you can call things like mockResolvedValue.

  ok: false,
  error: 'too_many_attachments',

// In this example, say will throw an error if Slack's response isn't ok
expect(bot.say('This will error')).rejects.toEqual({
  error: 'Oops, Something happened',


For proper typings, you must setup your tests a little differently. We use typescript, so you can always refer to our tests, but here's an example.

import {
} from '@slack-wrench/jest-mock-web-client';
import Bot from './bot';

describe('Your App', () => {
  let bot: Bot;
  let client: MockWebClient; // Notice this typing instead of `WebClient`

  beforeEach(() => {
    // We need to use `MockedWebClient` instead of `WebClient` for proper typings
    bot = new Bot();
    client = MockedWebClient.mock.instances[0];