npm package discovery and stats viewer.

Discover Tips

  • General search

    [free text search, go nuts!]

  • Package details

    pkg:[package-name]

  • User packages

    @[username]

Sponsor

Optimize Toolset

I’ve always been into building performant and accessible sites, but lately I’ve been taking it extremely seriously. So much so that I’ve been building a tool to help me optimize and monitor the sites that I build to make sure that I’m making an attempt to offer the best experience to those who visit them. If you’re into performant, accessible and SEO friendly sites, you might like it too! You can check it out at Optimize Toolset.

About

Hi, 👋, I’m Ryan Hefner  and I built this site for me, and you! The goal of this site was to provide an easy way for me to check the stats on my npm packages, both for prioritizing issues and updates, and to give me a little kick in the pants to keep up on stuff.

As I was building it, I realized that I was actually using the tool to build the tool, and figured I might as well put this out there and hopefully others will find it to be a fast and useful way to search and browse npm packages as I have.

If you’re interested in other things I’m working on, follow me on Twitter or check out the open source projects I’ve been publishing on GitHub.

I am also working on a Twitter bot for this site to tweet the most popular, newest, random packages from npm. Please follow that account now and it will start sending out packages soon–ish.

Open Software & Tools

This site wouldn’t be possible without the immense generosity and tireless efforts from the people who make contributions to the world and share their work via open source initiatives. Thank you 🙏

© 2024 – Pkg Stats / Ryan Hefner

jest-mock-extended

v3.0.5

Published

Type safe mocking extensions for jest

Downloads

3,568,478

Readme

jest-mock-extended

Type safe mocking extensions for Jest 🃏

Build Status Coverage Status npm version License: MIT npm downloads

Features

  • Provides complete Typescript type safety for interfaces, argument types and return types
  • Ability to mock any interface or object
  • calledWith() extension to provide argument specific expectations, which works for objects and functions.
  • Extensive Matcher API compatible with Jasmine matchers
  • Supports mocking deep objects / class instances.
  • Familiar Jest like API

Installation

npm install jest-mock-extended --save-dev

or

yarn add jest-mock-extended --dev

Example

import { mock } from 'jest-mock-extended';

interface PartyProvider {
   getPartyType: () => string;
   getSongs: (type: string) => string[]
   start: (type: string) => void;
}

describe('Party Tests', () => {
   test('Mock out an interface', () => {
       const mock = mock<PartyProvider>();
       mock.start('disco party');
       
       expect(mock.start).toHaveBeenCalledWith('disco party');
   });
   
   
   test('mock out a return type', () => {
       const mock = mock<PartyProvider>();
       mock.getPartyType.mockReturnValue('west coast party');
       
       expect(mock.getPartyType()).toBe('west coast party');
   });

    test('throwing an error if we forget to specify the return value')
        const mock = mock<PartyProvider>(
            {},
            {
                fallbackMockImplementation: () => {
                    throw new Error('not mocked');
                },
            }
        );

        expect(() => mock.getPartyType()).toThrowError('not mocked');
    });

Assigning Mocks with a Type

If you wish to assign a mock to a variable that requires a type in your test, then you should use the MockProxy<> type given that this will provide the apis for calledWith() and other built-in jest types for providing test functionality.

import { MockProxy, mock } from 'jest-mock-extended';

describe('test', () => {
    let myMock: MockProxy<MyInterface>;

    beforeEach(() => {
        myMock = mock<MyInterface>();
    })

    test(() => {
         myMock.calledWith(1).mockReturnValue(2);
         ...
    })
});

calledWith() Extension

jest-mock-extended allows for invocation matching expectations. Types of arguments, even when using matchers are type checked.

const provider = mock<PartyProvider>();
provider.getSongs.calledWith('disco party').mockReturnValue(['Dance the night away', 'Stayin Alive']);
expect(provider.getSongs('disco party')).toEqual(['Dance the night away', 'Stayin Alive']);

// Matchers
provider.getSongs.calledWith(any()).mockReturnValue(['Saw her standing there']);
provider.getSongs.calledWith(anyString()).mockReturnValue(['Saw her standing there']);

You can also use mockFn() to create a jest.fn() with the calledWith extension:

 type MyFn = (x: number, y: number) => Promise<string>;
 const fn = mockFn<MyFn>();
 fn.calledWith(1, 2).mockReturnValue('str');

Clearing / Resetting Mocks

jest-mock-extended exposes a mockClear and mockReset for resetting or clearing mocks with the same functionality as jest.fn().

import { mock, mockClear, mockReset } from 'jest-mock-extended';

describe('test', () => {
   const mock: UserService = mock<UserService>();
   
   beforeEach(() => {
      mockReset(mock); // or mockClear(mock)
   });
   ...
})

Deep mocks

If your class has objects returns from methods that you would also like to mock, you can use mockDeep in replacement for mock.

import { mockDeep } from 'jest-mock-extended';

const mockObj: DeepMockProxy<Test1> = mockDeep<Test1>();
mockObj.deepProp.getNumber.calledWith(1).mockReturnValue(4);
expect(mockObj.deepProp.getNumber(1)).toBe(4);

if you also need support for properties on functions, you can pass in an option to enable this

import { mockDeep } from 'jest-mock-extended';

const mockObj: DeepMockProxy<Test1> = mockDeep<Test1>({ funcPropSupport: true });
mockObj.deepProp.calledWith(1).mockReturnValue(3)
mockObj.deepProp.getNumber.calledWith(1).mockReturnValue(4);

expect(mockObj.deepProp(1)).toBe(3);
expect(mockObj.deepProp.getNumber(1)).toBe(4);

Can can provide a fallback mock implementation used if you do not define a return value using calledWith.

import { mockDeep } from 'jest-mock-extended';
const mockObj = mockDeep<Test1>({
    fallbackMockImplementation: () => {
        throw new Error('please add expected return value using calledWith');
    },
});
expect(() => mockObj.getNumber()).toThrowError('not mocked');

Available Matchers

| Matcher | Description | |-----------------------|-----------------------------------------------------------------------| |any() | Matches any arg of any type. | |anyBoolean() | Matches any boolean (true or false) | |anyString() | Matches any string including empty string | |anyNumber() | Matches any number that is not NaN | |anyFunction() | Matches any function | |anyObject() | Matches any object (typeof m === 'object') and is not null | |anyArray() | Matches any array | |anyMap() | Matches any Map | |anySet() | Matches any Set | |isA(class) | e.g isA(DiscoPartyProvider) | |includes('value') | Checks if value is in the argument array | |containsKey('key') | Checks if the key exists in the object | |containsValue('value') | Checks if the value exists in an object | |has('value') | checks if the value exists in a Set | |notNull() | value !== null | |notUndefined() | value !== undefined | |notEmpty() | value !== undefined && value !== null && value !== '' | |captor() | Used to capture an arg - alternative to mock.calls[0][0] |

Writing a Custom Matcher

Custom matchers can be written using a MatcherCreator

import { MatcherCreator, Matcher } from 'jest-mock-extended';

// expectedValue is optional
export const myMatcher: MatcherCreator<MyType> = (expectedValue) => new Matcher((actualValue) => {
    return (expectedValue === actualValue && actualValue.isSpecial);
});

By default, the expected value and actual value are the same type. In the case where you need to type the expected value differently than the actual value, you can use the optional 2 generic parameter:

import { MatcherCreator, Matcher } from 'jest-mock-extended';

// expectedValue is optional
export const myMatcher: MatcherCreator<string[], string> = (expectedValue) => new Matcher((actualValue) => {
    return (actualValue.includes(expectedValue));
});