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Karma vs Mocha: What are the differences?

Introduction

Here, we will present the key differences between Karma and Mocha, two popular JavaScript testing frameworks.

  1. Test Runner and Browser Integration: Karma acts as a test runner and provides seamless browser integration, allowing you to run tests on multiple browsers simultaneously. Mocha, on the other hand, is a test framework, but it doesn't have built-in support for browser automation and requires additional tools like WebDriver for running tests in different browsers.

  2. Testing Styles:

    • Karma primarily focuses on running tests written in various testing frameworks like Mocha, Jasmine, or QUnit, providing a test runner for these frameworks to execute tests in a browser environment.
    • Mocha is a more comprehensive testing framework that provides a syntax for writing tests, assertion libraries, and supports different styles of testing like BDD (Behavior-Driven Development) and TDD (Test-Driven Development) out of the box.
  3. Parallel Execution: Karma allows parallel execution of tests across multiple browsers, improving test execution time for large test suites. Mocha, however, doesn't offer parallel execution by default and will run tests sequentially.

  4. Code Coverage: Karma includes built-in code coverage reports, which can be generated during test execution, giving insights into the percentage of code covered by tests. Mocha itself doesn't provide code coverage functionality, but it can be integrated with other tools like Istanbul to generate code coverage reports.

  5. Browser Refresh: Karma has a live-reload feature that automatically refreshes the browsers whenever the test or source code changes. Mocha doesn't have this functionality, requiring you to manually refresh the browser or use additional tools like nodemon.

  6. Integration with Task Runners: Karma integrates well with task runners like Grunt or Gulp, allowing you to automate test execution along with other development tasks. Mocha, being a test framework, can also be integrated with task runners, but it requires additional configuration and setup.

In summary, Karma offers browser integration, parallel execution, code coverage, automatic browser refresh, and seamless integration with task runners. On the other hand, Mocha provides a comprehensive testing framework with different testing styles and can be integrated with Karma for browser testing.

Decisions about Karma and Mocha

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 Karma
Pros of Mocha
  • 61
    Test Runner
  • 35
    Open source
  • 27
    Continuous Integration
  • 22
    Great for running tests
  • 18
    Test on Real Devices
  • 11
    Backed by google
  • 5
    Easy Debugging
  • 2
    Remote Control
  • 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 Karma
Cons of Mocha
  • 1
    Slow, because tests are run in a real browser
  • 1
    Requires the use of hacks to find tests dynamically
  • 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 Karma?

Karma is not a testing framework, nor an assertion library. Karma just launches a HTTP server, and generates the test runner HTML file you probably already know from your favourite testing framework. So for testing purposes you can use pretty much anything you like.

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 companies use Karma?
What companies use Mocha?
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What tools integrate with Karma?
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What are some alternatives to Karma and Mocha?
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.
Jest
Jest provides you with multiple layers on top of Jasmine.
Protractor
Protractor is an end-to-end test framework for Angular and AngularJS applications. Protractor runs tests against your application running in a real browser, interacting with it as a user would.
Git
Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency.
GitHub
GitHub is the best place to share code with friends, co-workers, classmates, and complete strangers. Over three million people use GitHub to build amazing things together.
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