How to store Mocha test output in console?

I have an endpoint that runs mocha tests and I want to get the output of those tests and send it back to the client. Right now, I have:

exports.testApi = function (req, res) {
  var mocha = new Mocha();

  mocha.addFile('server/api/user/user.spec');
  // I want to get the output of mocha.run
  mocha.run(function (failures) {
    console.log('failures: ' + failures);
    return res.status(200).json({}});
  })
};

I've looked around and I can't seem to grasp how to use stdout to get the results on the console...