https://github.com/webpack/karma-webpack
npm install --save-dev karma-webpack
// karma.conf.js  --  karma configuration
// if you import your existing 'webpack.config.js' setup here,
// be sure to read the note about 'entry' below.
module.exports = function(config) {
    config.set({
        // ... normal karma configuration
        files: [
            // all files ending in "_test"
            'test/*_test.js',
            'test/**/*_test.js'
            // each file acts as entry point for the webpack configuration
        ],
        preprocessors: {
            // add webpack as preprocessor
            'test/*_test.js': ['webpack'],
            'test/**/*_test.js': ['webpack']
        },
        webpack: {
            // you don't need to specify the entry option because
            // karma watches the test entry points
            // webpack watches dependencies
            // ... remainder of webpack configuration (or import)
        },
        webpackMiddleware: {
            // webpack-dev-middleware configuration
            // i.e.
            noInfo: true,
            // and use stats to turn off verbose output
            stats: {
                // options i.e. 
                chunks: false
            }
        },
        plugins: [
            require("karma-webpack")
        ]
    });
};
For additional information about webpackMiddleware.stats options see Stats Options
This configuration is more performant, but you cannot run single test anymore (only the complete suite).
The above configuration generates a webpack bundle for each test. For many testcases this can result in many big files. The alterative configuration creates a single bundle with all testcases.
        files: [
            // only specify one entry point
            // and require all tests in there
            'test/test_index.js'
        ],
        preprocessors: {
            // add webpack as preprocessor
            'test/test_index.js': ['webpack']
        },
// test/test_index.js
// require all modules ending in "_test" from the
// current directory and all subdirectories
var testsContext = require.context(".", true, /_test$/);
testsContext.keys().forEach(testsContext);
Every test file is required using the require.context and compiled with webpack into one test bundle.
You can use the karma-sourcemap-loader to get the source maps generated for your test bundle.
npm install --save-dev karma-sourcemap-loader
And then add it to your preprocessors
preprocessors: {
    'test/test_index.js': ['webpack', 'sourcemap']
}
And tell webpack to generate sourcemaps
webpack: {
  // ...
    devtool: 'inline-source-map'
}
This is the full list of options you can specify in your Karma config.
Webpack configuration.
Configuration for webpack-dev-middleware.
Copyright 2014-2015 Tobias Koppers
    © 2012–2015 Tobias Koppers
Licensed under the MIT License.
    https://webpack.github.io/docs/usage-with-karma.html