Karma Test Runner

Common errors

• No captured browser, open http://localhost:9876/

  cause The Karma server started successfully, but no browser instance connected to it. This can happen if a browser launcher is missing, misconfigured, or if the browser failed to launch.
  fix Verify that you have the necessary browser launcher installed (e.g., `karma-chrome-launcher`), that it's listed in the `browsers` array of your `karma.conf.js`, and that no firewall or system setting is preventing the browser from launching or connecting to the Karma server.

• Can not load "Chrome" browser! Are you missing a plugin for it?

  cause Karma cannot find the necessary plugin to launch the specified browser (e.g., 'Chrome', 'Firefox', 'Safari').
  fix Install the corresponding Karma browser launcher package (e.g., `npm install --save-dev karma-chrome-launcher`) and ensure it's listed in your `karma.conf.js` file, typically in the `plugins` array if manually specified, or implicitly used if added to `browsers`.

• Can not load "jasmine" framework! Are you missing a plugin for it?

  cause The testing framework specified in your `karma.conf.js` (e.g., 'jasmine', 'mocha', 'qunit') does not have a corresponding Karma plugin installed.
  fix Install the correct Karma plugin for your chosen framework (e.g., `npm install --save-dev karma-jasmine`) and ensure it's included in the `frameworks` array within your `karma.conf.js`.

Warnings

• deprecated Karma is officially deprecated. The project will no longer receive new features or general bug fixes. While critical security fixes will continue for a limited period, users are strongly encouraged to migrate to modern alternatives.
  Fix: Migrate your testing setup to current alternatives like Web Test Runner, Jest, Vitest, or `jasmine-browser-runner`. Refer to the Karma README and Angular blog for migration guides.
• gotcha Karma requires Node.js version >= 10. Using older Node.js versions will lead to installation and runtime failures. Using very new, unsupported Node.js versions might also lead to compatibility issues, particularly with older plugins.
  Fix: Ensure your Node.js environment meets the `engines` requirement. It is recommended to use an actively maintained LTS version of Node.js for stability.
• breaking A malicious update to the `colors` package (a dependency of `karma`) in January 2022 introduced potential supply chain vulnerabilities, leading to corrupted output or system issues for users who pulled specific versions.
  Fix: Upgrade Karma to version `6.3.17` or higher, which includes an update to a maintained version of the `colors` package, mitigating this security risk.
• breaking An 'Open Redirect Vulnerability' was present in Karma, which could allow an attacker to redirect users to arbitrary external URLs if certain conditions were met.
  Fix: Upgrade Karma to version `6.3.16` or higher to receive the fix for this security vulnerability.
• gotcha Karma's configuration file (`karma.conf.js`) is fundamentally designed for CommonJS syntax (`module.exports = function(config) { ... }`). Attempting to use ESM `import`/`export` syntax directly in this file will lead to syntax errors or unexpected behavior, even in Node.js environments configured for ESM.
  Fix: Always use CommonJS `require()` and `module.exports` syntax in `karma.conf.js`. If you need to integrate ESM modules, consider transpiling your configuration or using a wrapper script.

Install

• npm install karma npm
• yarn add karma yarn
• pnpm add karma pnpm

Imports

• Server
  wrong:

  import { Server } from 'karma';

  correct:

  const Server = require('karma').Server;

  For programmatic control of the Karma server. Karma is a CommonJS module, so `require()` is the standard way to import its components in Node.js.
• config
  wrong:

  import { config } from 'karma';

  correct:

  const config = require('karma').config;

  For resolving Karma configuration files programmatically within a Node.js environment.
• runner
  wrong:

  import { runner } from 'karma';

  correct:

  const runner = require('karma').runner;

  Provides methods like `runner.run()` to programmatically start a test run against an already running Karma server.

Quickstart

This quickstart sets up a basic `karma.conf.js` using Jasmine and ChromeHeadless. To run, first install `karma`, `karma-jasmine`, `jasmine-core`, and `karma-chrome-launcher` (`npm install -D karma karma-jasmine jasmine-core karma-chrome-launcher`), then execute `npx karma start`.

// karma.conf.js
module.exports = function(config) {
  config.set({
    frameworks: ['jasmine'],
    files: [
      'src/**/*.js',
      'test/**/*.js'
    ],
    exclude: [],
    preprocessors: {},
    reporters: ['progress'],
    port: 9876,
    colors: true,
    logLevel: config.LOG_INFO,
    autoWatch: true,
    browsers: ['ChromeHeadless'], // Ensure karma-chrome-launcher is installed
    singleRun: false,
    concurrency: Infinity
  });
};

// test/example.test.js
describe('A simple test', function() {
  it('should pass', function() {
    expect(true).toBe(true);
  });
});