webpack-dev-server "mocha!./cover-my-client-tests.js" --options webpackOptions.js
// webpackOptions.js
module.exports = {
    // your webpack options
    output: "bundle.js",
    publicPrefix: "/",
    debug: true,
    includeFilenames: true,
    watch: true,
    // the coverjs loader binding
    postLoaders: [{
        test: "", // every file
        exclude: [
            "node_modules.chai",
            "node_modules.coverjs-loader",
            "node_modules.webpack.buildin"
        ],
        loader: "coverjs-loader"
    }]
}
 // cover-my-client-tests.js
require("./my-client-tests");
after(function() {
    require("cover-loader").reportHtml();
});
 See the-big-test for an example.
You don't have to combine it with the mocha loader, it's independent. So if you want to cover a normal app usage, you can do so. The reportHtml function just appends the output to the body.
MIT (http://www.opensource.org/licenses/mit-license.php)
    © JS Foundation and other contributors
Licensed under the Creative Commons Attribution License 4.0.
    https://webpack.js.org/loaders/coverjs-loader