from Gruntfile.js

karma: {
            unit: {
                configFile: 'karma.conf.js',
                singleRun: true
            },
            headless: {
                configFile: 'karma.conf.js',
                singleRun: true,
                browsers: ['PhantomJS']
            },
            watch: {
                configFile: 'karma.conf.js',
                background: true,
                reporters: ['progress']
            }
        }