Gulp + Karma: Karma won't stop

Question

I am running Karma with Gulp, something like this:

gulp.start(`karma`);

And then:

module.exports = (gulp, plugins) =>
  gulp.task('karma', done => {
    plugins.util.log('Testing with Karma');
    const server = new Server({
      configFile: path.join(__dirname, '..', '..', 'config/karma.conf.js'),
      singleRun: true
    }, done);
    server.start();
  });

Karma is running and my tests are passing, but it will not stop (stack with the "success" message).

I read this issue, which seems exactly like my case, but it seems to be solved. I also run this example, which seems to be running ok. The only difference (as far as I can tell), is that I run the command using gulp.start (I am writing a node module which should be running as a cli), and the example is running directly from package.json using gulp test.

What am I doing wrong here?