Pass in local browser names via command line `wdio --caps=chrome,firefox`

wdio.conf.js

const argv = require('yargs').argv;

let capabilities = [
  {
    browserName: 'chrome',
  },
  {
    browserName: 'firefox',
  },
  {
    browserName: 'safari',
  },
];

if (argv.caps) {
  // dynamically build out the capabilities
  const browsers = argv.caps.split(',');
  capabilities = browsers.map(browserName => {
    return {browserName};
  });
}

const wdioConfig = {
  ...
  capabilities,
  ...
}

exports.config = wdioConfig;