having
// config.js
module.exports = {
  projects: [
    'non_existing_path/',
    'another_non_existing_path/',
  ],
}; 
and running
will not throw, but try to run jest with some incorrect configuration, which makes it very frustrating to debug.
also
jest --config config.js --showConfig
 
will not print the accurate config (it'll only print one projectConfig and one globalConfig)