function createWebpackConfig(testAppDir, outputDirName = '', command, argv = {}) {
    argv._ = [command];
    argv.context = testAppDir;
    const runtimeConfig = parseRuntime(
        argv,
        testAppDir
    );

    const config = new WebpackConfig(runtimeConfig);

    const outputPath = path.join(testAppDir, outputDirName);
    // allows us to create a few levels deep without issues
    fs.mkdirsSync(outputPath);
    config.setOutputPath(outputPath);

    return config;
}
@param {string} testAppDir The dir from calling createTestAppDir()
@param {string} outputDirName
@param {string} command The encore command name (e.g. dev)
@param {object} argv Additional argv commands
@returns {WebpackConfig}