karma-rollup-plugin

0.2.4 verified Mon Apr 27 auth: no javascript maintenance

A Karma preprocessor plugin that integrates Rollup for on-the-fly bundling and ES2015+ transpilation in test environments. Current version is 0.2.4 (stable, but rarely updated). It supports Rollup plugins, source maps (inline), and multiple ES versions via Babel or Buble. Compared to alternatives like karma-rollup-preprocessor, this plugin is simpler, more actively maintained at the time, and more aligned with the Rollup ecosystem. However, it lacks modern Rollup features and may not work with Rollup >=1.0.

Common errors

error Error: Cannot find module 'rollup' ↓

cause Rollo is not installed or is a missing peer dependency.

fix

Run: npm install rollup --save-dev

error TypeError: rollup.rollup is not a function ↓

cause Incompatible Rollup version >=1.0 where API changed.

fix

Install Rollup 0.x: npm install rollup@0.68.2 --save-dev

error WARN: 'umd' format requires a module name. Use the 'moduleName' option. ↓

cause Using 'umd' format without 'moduleName' in rollupPreprocessor.

fix

Add moduleName to rollupPreprocessor or switch to 'iife'.

Warnings

breaking No support for Rollup >=1.0 due to API changes. ↓

fix Upgrade to a maintained fork or use karma-rollup-preprocessor with Rollup compatibility.

deprecated Package is no longer actively maintained; last release was years ago. ↓

fix Consider using @open-wc/karma-esm or karma-rollup-preprocessor.

gotcha Using 'umd' format without a module name throws a warning and may produce unexpected results. ↓

fix Always specify a module name when using 'umd', or use 'iife' for tests.

gotcha Source maps must be 'inline' because Karma expects them inlined for proper debugging. ↓

fix Set sourceMap: 'inline' in rollupPreprocessor config.

Install

npm install karma-rollup-plugin

yarn add karma-rollup-plugin

pnpm add karma-rollup-plugin

Imports

rollupPreprocessor (Karma config key)
wrong
```
rollupPreprocessor: require('karma-rollup-plugin')
```
correct
```
// In karma.conf.js
rollupPreprocessor: { /* options */ }
```
The plugin is automatically loaded by Karma. No explicit require() in karma.conf.js.
Plugin as a module (programmatic use)
wrong
```
import karmaRollup from 'karma-rollup-plugin';
```
correct
```
const karmaRollup = require('karma-rollup-plugin');
```
Plugin exports a function for programmatic configuration, but typically used via Karma config.

Preprocessor in preprocessors

wrong

preprocessors: { 'test/**/*.js': ['karma-rollup-plugin'] }

correct

preprocessors: { 'test/**/*.js': ['rollup'] }

Use the short name 'rollup', not the package name.

Quickstart

Configures Karma to use the rollup preprocessor for test files, with Rollup and Buble plugin for transpilation.

// karma.conf.js
module.exports = function (config) {
  config.set({
    basePath: '',
    frameworks: ['jasmine'],
    files: [
      'test/**/*.spec.js'
    ],
    preprocessors: {
      'test/**/*.spec.js': ['rollup']
    },
    rollupPreprocessor: {
      plugins: [ require('rollup-plugin-buble')() ],
      format: 'iife',
      sourceMap: 'inline'
    },
    reporters: ['progress'],
    port: 9876,
    colors: true,
    logLevel: config.LOG_INFO,
    autoWatch: true,
    browsers: ['ChromeHeadless'],
    singleRun: false
  });
};