Karma doesn't exit properly when using public api with the finish callback

Using Karma’s server public API with a done callback makes the whole node process “stuck” - there are probably some event listeners that prevent node process from exiting properly. A simple reproduce scenario:

var karma = require('karma').server;

karma.start({
  //transports: ['websocket', 'xhr-polling', 'jsonp-polling'],
  browsers: ['Chrome'],
  frameworks: ['jasmine'],
  files: [
    'src/**/*.js',
    'test/**/*.spec.js'
  ],
  singleRun: true
}, function(karmaExitCode) {
  console.log('Karma exited with ', karmaExitCode);
  console.log('but the process will never exit...');
});

Interestingly, removing the flash from the list of transports make the Karma exit after a while (~20s after test are finished on my machine).

There is a small repo with the reproduce scenario here: https://github.com/karma-runner/gulp-karma/blob/exit_pb/exitTest.js I will be digging into the topic but any help from someone more knowledgeable about Karma internals would be highly appreciated.

[lazd]

process.exit() is fatal, so that won’t work.

[jnwu]

As a workaround, I am forcing the karma server to be executed in a separate process via ‘gulp-multi-process’

gulp.task('test', () => {
    const config = parseConfig(path.resolve('test/karma.conf.js'));
    const server = new karma.Server(config);
    server.start();
});

gulp.task('multi', (cb) => {
    return multiProcess(['test'], cb);
});

gulp.task('watch', () => {
    gulp.watch(files, ['multi']);
});

In addition my karma config has autoWatch off, and singleRun on. Hence, I am using gulp to watch my files and delegating all the test tasks (including report generation) to karma.