i'm trying pass grep argument karma-mocha plugin pass mocha , run tests match grep . command line this: ./node_modules/.bin/karma run -- --grep='one' however, karma goes on tests, in same way if not use --grep . according karma run --help , after -- should client arguments. (it referred clientarg in , in discussions how run karma run .) tried small project without requirejs , worked. seems adding requirejs causes problem. here small setup reproduces issue: karma.conf.js : module.exports = function(config) { config.set({ basepath: '', frameworks: ['mocha', 'requirejs'], files: [ 'test-main.js', { pattern: 'test/**/*.js', included: false } ], exclude: [], preprocessors: {}, reporters: ['progress'], port: 9876, colors: true, loglevel: config.log_info, autowatch: false, browsers: ['chrome'], singlerun: false, concurrency: infinity }); }...