karma.conf.js

module.exports = function (config) {
    config.set({
        browsers: ["Chrome"], // run in Chrome
        singleRun: true, // just run once by default
        frameworks: ["mocha"], // use the mocha test framework
        files: [{ pattern: "webpack.tests.js", watched: false }],
        preprocessors: {
            "webpack.tests.js": ["webpack", "sourcemap"],
        },
        reporters: ["dots"], // report results in this format
        webpack: {
            // kind of a copy of your webpack config
            devtool: "inline-source-map", // just do inline source maps instead of the default
            mode: "development",
            module: {
                rules: [
                    {
                        loader: "babel-loader",
                        exclude: /node_modules/,
                        test: /\.(js|jsx)$/,
                        query: {
                            presets: [
                                "@babel/preset-env",
                                "@babel/preset-react",
                            ],
                        },
                        resolve: {
                            extensions: [".js", ".jsx"],
                        },
                    },
                    {
                        test: /\.scss$/,
                        use: [
                            {
                                loader: "style-loader",
                            },
                            {
                                loader: "css-loader",
                            },
                            {
                                loader: "sass-loader",
                            },
                        ],
                    },
                ],
            },
        },
        plugins: [
            require("karma-mocha"),
            require("karma-webpack"),
            require("karma-sourcemap-loader"),
            require("karma-chrome-launcher"),
        ],
    });
};