How to unit test a function which calls another that returns a promise?

I have a node.js app using express 4 and this is my controller:

var service = require('./category.service');

module.exports = {
  findAll: (request, response) => {
    service.findAll().then((categories) => {
      response.status(200).send(categories);
    }, (error) => {
      response.status(error.statusCode || 500).json(error);
    });
  }
};

It calls my service which returns a promise. Everything works but I am having trouble when trying to unit test it.

Basically, I would like to make sure that based on what my service returns, I flush the response with the right status code and body.

So with mocha and sinon it looks something like:

it('Should call service to find all the categories', (done) => {
    // Arrange
    var expectedCategories = ['foo', 'bar'];

    var findAllStub = sandbox.stub(service, 'findAll');
    findAllStub.resolves(expectedCategories);

    var response = {
       status: () => { return response; },
       send: () => {}
    };
    sandbox.spy(response, 'status');
    sandbox.spy(response, 'send');

    // Act
    controller.findAll({}, response);

    // Assert
    expect(findAllStub.called).to.be.ok;
    expect(findAllStub.callCount).to.equal(1);
    expect(response.status).to.be.calledWith(200); // not working
    expect(response.send).to.be.called; // not working
    done();
});

I have tested my similar scenarios when the function I am testing returns itself a promise since I can hook my assertions in the then.

I also have tried to wrap controller.findAll with a Promise and resolve it from the response.send but it didn't work neither.