msw vs sinon vs nock vs mockttp
HTTP Mocking and Testing Libraries
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HTTP Mocking and Testing Libraries

HTTP mocking and testing libraries are essential tools in web development that allow developers to simulate server responses and test how applications handle various scenarios without relying on actual network requests. These libraries help in creating a controlled testing environment, enabling developers to ensure their applications behave correctly under different conditions, such as error responses, timeouts, or specific data formats. They are particularly useful in unit testing and integration testing, where isolating components from external dependencies is crucial for reliable tests.

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msw8,540,22617,5534.86 MB5425 days agoMIT
sinon8,093,7969,7622.22 MB51a month agoBSD-3-Clause
nock4,884,76513,069185 kB885 months agoMIT
mockttp304,5718441.84 MB403 months agoApache-2.0
Feature Comparison: msw vs sinon vs nock vs mockttp

Flexibility

  • msw:

    msw (Mock Service Worker) offers flexibility by allowing you to define request handlers directly in your application code. It intercepts network requests at the service worker level, enabling you to mock both REST and GraphQL APIs seamlessly. This approach allows for more realistic testing as it mimics actual network behavior.

  • sinon:

    sinon provides flexibility in mocking and spying on functions, but it is not specifically designed for HTTP requests. It can be used alongside other libraries to mock HTTP calls, but it requires additional setup to achieve similar functionality as dedicated HTTP mocking libraries.

  • nock:

    nock is flexible in that it allows you to intercept HTTP requests in Node.js and define how they should respond. However, it is primarily focused on Node.js environments and may not be as versatile for browser-based applications compared to other libraries.

  • mockttp:

    mockttp provides a highly flexible API that allows you to define custom responses based on request parameters, making it suitable for testing various edge cases and scenarios. You can easily mock different HTTP methods, headers, and response statuses, giving you full control over the testing environment.

Use Cases

  • msw:

    msw is best suited for frontend applications where you want to mock API calls during development and testing. It allows you to develop and test your application without needing a backend server, making it easier to iterate on frontend features without waiting for backend changes.

  • sinon:

    sinon is primarily used for spying, stubbing, and mocking functions in JavaScript. While it can be used to mock HTTP requests, it is not specialized for that purpose. It is best used in conjunction with other libraries for comprehensive testing.

  • nock:

    nock is designed for Node.js applications and is great for testing backend services that make HTTP requests. It allows you to simulate external API responses, making it easier to test how your application handles different scenarios without relying on live services.

  • mockttp:

    mockttp is particularly useful for testing Node.js applications that rely heavily on HTTP requests. It is ideal for unit tests where you want to isolate the component under test from external services and simulate various server responses without making real network calls.

Integration

  • msw:

    msw integrates well with various frontend frameworks and libraries, including React, Vue, and Angular. It allows you to define request handlers in a way that keeps your application logic clean and separate from your testing logic, enhancing maintainability.

  • sinon:

    sinon can be integrated with any testing framework, but it requires more manual setup for mocking HTTP requests. It is often used alongside other libraries to provide a complete testing solution.

  • nock:

    nock integrates well with Node.js testing frameworks, allowing you to mock HTTP requests directly in your tests. It is straightforward to use with Mocha or Jest, but it may require additional setup for more complex scenarios.

  • mockttp:

    mockttp integrates seamlessly with testing frameworks like Jest and Mocha, allowing you to set up and tear down mocks easily within your test suites. Its design encourages a clean separation of concerns, making tests easier to read and maintain.

Learning Curve

  • msw:

    msw has a moderate learning curve, particularly for developers new to service workers. However, once understood, it provides powerful capabilities for mocking network requests in a way that closely resembles real-world scenarios.

  • sinon:

    sinon has a moderate learning curve, especially for developers unfamiliar with mocking and spying concepts. However, once you grasp its core functionalities, it becomes a powerful tool for testing.

  • nock:

    nock has a low learning curve for Node.js developers, as its API is simple and intuitive. However, it may require some familiarity with Node.js HTTP requests to use effectively.

  • mockttp:

    mockttp has a relatively low learning curve, especially for developers familiar with Node.js. Its API is straightforward, making it easy to get started with mocking HTTP requests quickly.

Community and Support

  • msw:

    msw has a strong community and is widely adopted in the frontend development ecosystem. Its documentation is comprehensive, and there are numerous tutorials and examples available to help developers get started.

  • sinon:

    sinon has a large user base and extensive documentation, making it a well-supported choice for JavaScript testing. Its long-standing presence in the community means that many resources and examples are available.

  • nock:

    nock has been around for a while and has a solid community, but its focus on Node.js may limit its audience compared to more versatile libraries. Documentation is available, but some users may find it lacking in examples.

  • mockttp:

    mockttp has a growing community and is actively maintained, with good documentation and examples available. This makes it easier for developers to find help and resources when needed.

How to Choose: msw vs sinon vs nock vs mockttp
  • mockttp:

    Choose mockttp if you need a lightweight and flexible HTTP mocking library specifically designed for testing Node.js applications. It allows you to create a mock server that can intercept requests and respond with predefined data, making it ideal for testing asynchronous code and handling complex scenarios.

Similar Npm Packages to msw

msw (Mock Service Worker) is a powerful library for mocking API requests in JavaScript applications. It allows developers to intercept network requests and provide custom responses, making it an invaluable tool for testing and development. By using service workers, msw can simulate a variety of scenarios, including error responses and delayed requests, without the need for a backend server. This capability helps ensure that applications can be tested and developed in isolation, leading to more robust and reliable code.

While msw is a great choice for mocking API requests, there are several alternatives available in the ecosystem:

  • axios-mock-adapter is a library specifically designed to work with axios, a popular HTTP client. It allows developers to easily mock requests made with axios by providing a simple API for defining request handlers and responses. If your application heavily relies on axios for making HTTP requests, axios-mock-adapter is a straightforward option for mocking those requests during testing.
  • fetch-mock is a library that provides a way to mock the Fetch API, which is commonly used for making network requests in modern web applications. It allows developers to define mock responses for specific requests, making it easier to test components that rely on the Fetch API. If your application uses the Fetch API and you need a simple way to mock network requests, fetch-mock is a solid choice.
  • nock is a powerful HTTP mocking library for Node.js. It allows developers to intercept and mock HTTP requests made by Node.js applications, making it particularly useful for testing backend services or APIs. nock provides a flexible API for defining request interceptors and responses, making it suitable for a wide range of testing scenarios. If you're working in a Node.js environment and need to mock HTTP requests, nock is a reliable option.

To see how msw compares with axios-mock-adapter, fetch-mock, and nock, check out the comparison: Comparing axios-mock-adapter vs fetch-mock vs msw vs nock.

Similar Npm Packages to sinon

sinon is a powerful standalone library for creating spies, mocks, and stubs in JavaScript applications. It is primarily used for testing purposes, allowing developers to replace parts of their code with controlled replacements that can simulate behaviors and track interactions. This makes it easier to test functions in isolation without relying on their dependencies. While sinon is a robust tool for testing, there are several alternatives in the JavaScript ecosystem that also provide testing capabilities. Here are a few notable alternatives:

  • chai is an assertion library for Node.js and browsers that can be paired with any testing framework. It provides a variety of assertion styles, including BDD (Behavior-Driven Development) and TDD (Test-Driven Development) styles, making it flexible for different testing preferences. While chai does not provide mocking or spying capabilities like sinon, it can be used alongside sinon to create comprehensive tests that include assertions and mocks.
  • jasmine is a behavior-driven development framework for testing JavaScript code. It comes with built-in support for spies, mocks, and assertions, making it a complete testing solution. Jasmine is particularly known for its easy-to-read syntax and ability to run tests in any JavaScript environment. If you prefer an all-in-one testing framework that includes mocking capabilities, jasmine is a solid choice.
  • jest is a popular testing framework developed by Facebook, known for its simplicity and powerful features. Jest includes built-in support for mocking, spying, and assertions, making it a comprehensive solution for testing JavaScript applications. It also offers features like snapshot testing and parallel test execution, which can significantly speed up the testing process. If you're looking for a modern testing framework that integrates well with React and other JavaScript libraries, jest is highly recommended.
  • mocha is a flexible testing framework that allows developers to choose their assertion library and mocking tools. While mocha itself does not provide built-in mocking capabilities, it can be easily integrated with sinon for spying and stubbing. Mocha's flexibility makes it a popular choice for developers who want to customize their testing setup according to their specific needs.

To see how sinon compares with chai, jasmine, jest, and mocha, check out the comparison: Comparing chai vs jasmine vs jest vs mocha vs sinon.

Similar Npm Packages to nock

nock is a powerful HTTP mocking library for Node.js that allows developers to intercept and mock HTTP requests in their tests. It is particularly useful for testing applications that rely on external APIs, as it enables developers to simulate various responses without actually making network calls. This can lead to faster tests and more reliable results, as tests can be run consistently without dependency on external services. While nock is a popular choice for HTTP mocking, there are several alternatives available in the ecosystem. Here are a few:

  • axios-mock-adapter is a library specifically designed for mocking HTTP requests made with the Axios library. It allows developers to easily set up mock responses for their Axios requests, making it a great choice for applications that use Axios for API calls. With a simple and intuitive API, axios-mock-adapter can help streamline testing by providing a way to simulate various scenarios and responses without needing to rely on actual network requests.
  • fetch-mock is a library for mocking fetch requests in JavaScript. It provides a flexible API for intercepting and mocking HTTP requests made with the Fetch API, making it ideal for testing applications that use fetch for data retrieval. fetch-mock allows developers to define custom responses, simulate network errors, and control the behavior of their fetch requests, making it a valuable tool for ensuring that applications behave as expected under various conditions.
  • mockttp is another HTTP mocking library that allows developers to create a mock server for testing HTTP requests. It supports both Node.js and browser environments and can be used to simulate a variety of HTTP responses. mockttp is particularly useful for testing applications that need to handle complex scenarios, such as streaming responses or handling different HTTP methods. Its ability to create a full mock server makes it a versatile option for developers looking to thoroughly test their applications.

To see how nock compares with axios-mock-adapter, fetch-mock, and mockttp, check out the comparison: Comparing axios-mock-adapter vs fetch-mock vs mockttp vs nock.

Similar Npm Packages to mockttp

mockttp is a powerful HTTP mocking library for Node.js and browser applications. It allows developers to create mock servers that can intercept and respond to HTTP requests, making it easier to test applications without relying on real network calls. This is particularly useful for unit testing and integration testing, where you want to isolate your tests from external dependencies. While mockttp provides robust features for mocking HTTP requests, there are several alternatives in the ecosystem that offer similar functionalities. Here are a few notable ones:

  • msw (Mock Service Worker) is a popular library for mocking API requests in both browser and Node.js environments. It uses Service Workers to intercept network requests, allowing developers to define request handlers that can respond with mock data. This approach enables a seamless testing experience, as it mimics the actual behavior of a server. msw is particularly beneficial for testing client-side applications, as it allows for easy integration with existing workflows and provides a realistic simulation of network interactions.
  • nock is another widely used HTTP mocking library for Node.js. It allows developers to intercept HTTP requests and provide predefined responses, making it ideal for testing applications that rely on external APIs. nock is particularly useful for unit tests, as it can help isolate tests from external services and ensure consistent results. Its straightforward API and ability to handle various HTTP methods and status codes make it a popular choice among developers looking to mock HTTP requests in their Node.js applications.
  • sinon is a versatile library for creating spies, stubs, and mocks in JavaScript. While it is not exclusively focused on HTTP mocking, it provides powerful tools for testing and mocking functions, including HTTP requests. Developers can use sinon to replace real HTTP calls with mock implementations, allowing for more controlled and predictable tests. If you're already using sinon for other aspects of your testing, it can be a convenient option for mocking HTTP requests as well.

To see how mockttp compares with msw, nock, and sinon, check out the comparison: Comparing mockttp vs msw vs nock vs sinon.

README for msw

The Mock Service Worker logo

Mock Service Worker

Industry standard API mocking for JavaScript.

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Features

  • Seamless. A dedicated layer of requests interception at your disposal. Keep your application's code and tests unaware of whether something is mocked or not.
  • Deviation-free. Request the same production resources and test the actual behavior of your app. Augment an existing API, or design it as you go when there is none.
  • Familiar & Powerful. Use Express-like routing syntax to intercept requests. Use parameters, wildcards, and regular expressions to match requests, and respond with necessary status codes, headers, cookies, delays, or completely custom resolvers.

"I found MSW and was thrilled that not only could I still see the mocked responses in my DevTools, but that the mocks didn't have to be written in a Service Worker and could instead live alongside the rest of my app. This made it silly easy to adopt. The fact that I can use it for testing as well makes MSW a huge productivity booster."

— Kent C. Dodds

Documentation

This README will give you a brief overview of the library, but there's no better place to start with Mock Service Worker than its official documentation.

Examples

Courses

We've partnered with Egghead to bring you quality paid materials to learn the best practices of API mocking on the web. Please give them a shot! The royalties earned from them help sustain the project's development. Thank you.

Browser

How does it work?

In-browser usage is what sets Mock Service Worker apart from other tools. Utilizing the Service Worker API, which can intercept requests for the purpose of caching, Mock Service Worker responds to intercepted requests with your mock definition on the network level. This way your application knows nothing about the mocking.

Take a look at this quick presentation on how Mock Service Worker functions in a browser:

What is Mock Service Worker?

How is it different?

  • This library intercepts requests on the network level, which means after they have been performed and "left" your application. As a result, the entirety of your code runs, giving you more confidence when mocking;
  • Imagine your application as a box. Every API mocking library out there opens your box and removes the part that does the request, placing a blackbox in its stead. Mock Service Worker leaves your box intact, 1-1 as it is in production. Instead, MSW lives in a separate box next to yours;
  • No more stubbing of fetch, axios, react-query, you-name-it;
  • You can reuse the same mock definition for the unit, integration, and E2E testing. Did we mention local development and debugging? Yep. All running against the same network description without the need for adapters or bloated configurations.

Usage example

// 1. Import the library.
import { http, HttpResponse } from 'msw'
import { setupWorker } from 'msw/browser'

// 2. Describe network behavior with request handlers.
const worker = setupWorker(
  http.get('https://github.com/octocat', ({ request, params, cookies }) => {
    return HttpResponse.json(
      {
        message: 'Mocked response',
      },
      {
        status: 202,
        statusText: 'Mocked status',
      },
    )
  }),
)

// 3. Start mocking by starting the Service Worker.
await worker.start()

Performing a GET https://github.com/octocat request in your application will result into a mocked response that you can inspect in your browser's "Network" tab:

Chrome DevTools Network screenshot with the request mocked

Tip: Did you know that although Service Worker runs in a separate thread, your request handlers execute entirely on the client? This way you can use the same languages, like TypeScript, third-party libraries, and internal logic to create the mocks you need.

Node.js

How does it work?

There's no such thing as Service Workers in Node.js. Instead, MSW implements a low-level interception algorithm that can utilize the very same request handlers you have for the browser. This blends the boundary between environments, allowing you to focus on your network behaviors.

How is it different?

  • Does not stub fetch, axios, etc. As a result, your tests know nothing about mocking;
  • You can reuse the same request handlers for local development and debugging, as well as for testing. Truly a single source of truth for your network behavior across all environments and all tools.

Usage example

Here's an example of using Mock Service Worker while developing your Express server:

import express from 'express'
import { http, HttpResponse } from 'msw'
import { setupServer } from 'msw/node'

const app = express()
const server = setupServer()

app.get(
  '/checkout/session',
  server.boundary((req, res) => {
    // Describe the network for this Express route.
    server.use(
      http.get(
        'https://api.stripe.com/v1/checkout/sessions/:id',
        ({ params }) => {
          return HttpResponse.json({
            id: params.id,
            mode: 'payment',
            status: 'open',
          })
        },
      ),
    )

    // Continue with processing the checkout session.
    handleSession(req, res)
  }),
)

This example showcases server.boundary() to scope request interception to a particular closure, which is extremely handy!

Sponsors

Mock Service Worker is trusted by hundreds of thousands of engineers around the globe. It's used by companies like Google, Microsoft, Spotify, Amazon, Netflix, and countless others. Despite that, it remains a hobby project maintained in a spare time and has no opportunity to financially support even a single full-time contributor.

You can change that! Consider sponsoring the effort behind one of the most innovative approaches around API mocking. Raise a topic of open source sponsorships with your boss and colleagues. Let's build sustainable open source together!

Golden sponsors

Become our golden sponsor and get featured right here, enjoying other perks like issue prioritization and a personal consulting session with us.

Learn more on our GitHub Sponsors profile.


GitHub Codacy Workleap Chromatic
StackBlitz

Silver sponsors

Become our silver sponsor and get your profile image and link featured right here.

Learn more on our GitHub Sponsors profile.


Replay Codemod Ryan Magoon

Bronze sponsors

Become our bronze sponsor and get your profile image and link featured in this section.

Learn more on our GitHub Sponsors profile.


Materialize Trigger.dev Vital

Awards & mentions

We've been extremely humbled to receive awards and mentions from the community for all the innovation and reach Mock Service Worker brings to the JavaScript ecosystem.

Technology Radar

Solution Worth Pursuing

Technology Radar (2020–2021)

Open Source Awards 2020

The Most Exciting Use of Technology

Open Source Awards (2020)

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