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Jest vs Mocha: What are the differences?

Key Differences between Jest and Mocha

Jest and Mocha are both popular JavaScript testing frameworks often used in web development. While they share some similarities, there are several key differences between the two.

  1. Testing Environment: Jest includes an out-of-the-box testing environment, making it easier to set up and use. On the other hand, Mocha requires additional setup and configuration to define and set up testing environments.

  2. Assertion Library: Jest comes bundled with its own assertion library, whereas Mocha does not include one out of the box. However, Mocha supports a wide range of assertion libraries like Chai, Should.js, and Expect.js, giving developers more flexibility in choosing their preferred library.

  3. Mocking and Spying: Jest offers built-in mocking and spying functionalities, making it easier to create and manage mocks and spies in tests. Mocha does not provide these features out of the box and requires additional libraries like Sinon.js to accomplish similar functionalities.

  4. Performance: Jest is known for its fast and parallelized test execution, making it suitable for larger projects with extensive test suites. Mocha, on the other hand, may be slower in comparison, especially when dealing with large test suites or running tests in parallel.

  5. Configuration: Jest comes with a pre-configured setup and requires minimal configuration, making it an ideal choice for projects with less complex testing needs. Mocha offers more flexibility but requires additional configuration to set up testing frameworks, assertion libraries, and other tools.

  6. Reporting: Jest provides detailed and user-friendly test reports out of the box. It offers a comprehensive overview of test results, including test coverage. Mocha, on the other hand, does not provide built-in test reporting, requiring the use of additional libraries or plugins for generating test reports.

In summary, Jest is a powerful testing framework that offers an easy setup, includes its own assertion library, built-in mocking and spying functionalities, and provides detailed test reports. On the other hand, Mocha offers more flexibility in terms of testing environment, assertion library choice, and configuration options, making it suitable for projects with specific requirements.

Decisions about Jest and Mocha
Ben Herbert
Lead Front End Developer at Crunch | 4 upvotes 路 44.2K views

We were able to combine multiple tools with Jest and React Testing Library (e.g. sinon, enzyme, chai). Jest has powerful cli options and increased performance including from parallel testing processes. Migrating was reasonably straight forward as there is a code transformation script to do most of the leg work. Jest's documentation is excellent.

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CypressCypressJestJest

As we all know testing is an important part of any application. To assist with our testing we are going to use both Cypress and Jest. We feel these tools complement each other and will help us get good coverage of our code. We will use Cypress for our end to end testing as we've found it quite user friendly. Jest will be used for our unit tests because we've seen how many larger companies use it with great success.

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Postman will be used to do integration testing with the backend API we create. It offers a clean interface to create many requests, and you can even organize these requests into collections. It helps to test the backend API first to make sure it's working before using it in the front-end. Jest can also be used for testing and is already embedded into React. Not only does it offer unit testing support in javascript, it can also do snapshot testing for the front-end to make sure components are rendering correctly. Enzyme is complementary to Jest and offers more functions such as shallow rendering. UnitTest will be used for Python testing as it is simple, has a lot of functionality and already built in with python. Sentry will be used for keeping track of errors as it is also easily integratable with Heroku because they offer it as an add-on. LogDNA will be used for tracking logs which are not errors and is also a Heroku add-on. Its good to have a separate service to record logs, monitor, track and even fix errors in real-time so our application can run more smoothly.

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We use Mocha for our FDA verification testing. It's integrated into Meteor, our upstream web application framework. We like how battle tested it is, its' syntax, its' options of reporters, and countless other features. Most everybody can agree on mocha, and that gets us half-way through our FDA verification and validation (V&V) testing strategy.

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Pros of Jest
Pros of Mocha
  • 36
    Open source
  • 32
    Mock by default makes testing much simpler
  • 23
    Testing React Native Apps
  • 20
    Parallel test running
  • 16
    Fast
  • 13
    Bundled with JSDOM to enable DOM testing
  • 8
    Mock by default screws up your classes, breaking tests
  • 7
    Out of the box code coverage
  • 7
    Promise support
  • 6
    One stop shop for unit testing
  • 3
    Great documentation
  • 2
    Assert Library Included
  • 1
    Built in watch option with interactive filtering menu
  • 1
    Preset support
  • 0
    Can be used for BDD
  • 0
    Karma
  • 137
    Open source
  • 102
    Simple
  • 81
    Promise support
  • 48
    Flexible
  • 29
    Easy to add support for Generators
  • 12
    For browser and server testing
  • 7
    Curstom assertion libraries
  • 5
    Works with Karma
  • 3
    No other better tools
  • 1
    Simple setup
  • 1
    Works with saucelabs
  • 1
    Lots of tutorials and help online
  • 1
    Default reporter is nice, clean, and itemized
  • 1
    Works with BrowserStack
  • 1
    Simple integration testing

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Cons of Jest
Cons of Mocha
  • 4
    Documentation
  • 4
    Ambiguous configuration
  • 3
    Difficult
  • 2
    Many bugs still not fixed months/years after reporting
  • 2
    Multiple error messages for same error
  • 2
    Difficult to run single test/describe/file
  • 2
    Ambiguous
  • 2
    Bugged
  • 1
    BeforeAll timing out makes all passing tests fail
  • 1
    Slow
  • 1
    Reporter is too general
  • 1
    Unstable
  • 1
    Bad docs
  • 1
    Still does't support .mjs files natively
  • 1
    Can't fail beforeAll to abort tests
  • 0
    Interaction with watch mode on terminal
  • 3
    Cannot test a promisified functions without assertion
  • 2
    No assertion count in results
  • 1
    Not as many reporter options as Jest

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What is Jest?

Jest provides you with multiple layers on top of Jasmine.

What is Mocha?

Mocha is a feature-rich JavaScript test framework running on node.js and the browser, making asynchronous testing simple and fun. Mocha tests run serially, allowing for flexible and accurate reporting, while mapping uncaught exceptions to the correct test cases.

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What are some alternatives to Jest and Mocha?
Selenium
Selenium automates browsers. That's it! What you do with that power is entirely up to you. Primarily, it is for automating web applications for testing purposes, but is certainly not limited to just that. Boring web-based administration tasks can (and should!) also be automated as well.
AVA
Even though JavaScript is single-threaded, IO in Node.js can happen in parallel due to its async nature. AVA takes advantage of this and runs your tests concurrently, which is especially beneficial for IO heavy tests. In addition, test files are run in parallel as separate processes, giving you even better performance and an isolated environment for each test file.
Enzyme
Enzyme is a JavaScript Testing utility for React that makes it easier to assert, manipulate, and traverse your React Components' output.
Jasmine
Jasmine is a Behavior Driven Development testing framework for JavaScript. It does not rely on browsers, DOM, or any JavaScript framework. Thus it's suited for websites, Node.js projects, or anywhere that JavaScript can run.
Cypress
Cypress is a front end automated testing application created for the modern web. Cypress is built on a new architecture and runs in the same run-loop as the application being tested. As a result Cypress provides better, faster, and more reliable testing for anything that runs in a browser. Cypress works on any front-end framework or website.
See all alternatives