testing events sinon node.js

I want testing my function and I stuck with mocking events. I don't know how mock event with sinon. This is my code when I stuck:

return pdfGenerator(invoice)
                            .then(content =>
                            {
                                const printer = new PdfMakePrinter(fonts);
                                let pdfDoc = {};
                                try {
                                    pdfDoc = printer.createPdfKitDocument(content);
                                } catch (error) {
                                    throw applicationException.new(applicationException.ERROR, 'Something bad in pdf content: ' + error);
                                }

                                let filepath = path.join(__dirname, '../REST/uploads/', filename);
                                let result = pdfDoc.pipe(fs.createWriteStream(filepath));
                                pdfDoc.end();
                                return new Promise(resolve =>
                                {
                                    result.on('finish', resolve);
                                })
                            })

Problem occured when I want test

result.on('finish',resolve);

This is my test:

let pdfGeneratorMock = sinon.stub();
let endMock = sinon.stub().callsFake(function ()
{
    return 0;
});
let pipeMock = sinon.spy();
let createPdfKitDocumentMock = sinon.spy(() =>
{
    return {
        end: endMock,
        pipe: pipeMock
    }
});
let pdfMakePrinterMock = sinon.spy(function ()
{
    return {
        createPdfKitDocument: createPdfKitDocumentMock
    }
});
let onMock = sinon.spy(function(text,callback){
    return callback();
});
let writeStreamMock = sinon.spy(() =>
{
    return {
        on: onMock
    }
});
let fs = {
    mkdirSync: sinon.spy(),
    createWriteStream: writeStreamMock
};
........

it('should call createPefKitDocument', function ()
  {
       expect(createPdfKitDocumentMock).callCount(1);
  });
it('should call fs.createWriteStream', function ()
{
    expect(writeStreamMock).callCount(1);
});

it('should call pipe', function ()
{
    expect(pipeMock).callCount(1);
});
it('should call end', function ()
{
    expect(endMock).callCount(1);
});

it('should call on', function ()
{

    expect(onMock).callCount(1);
});

Test not pass to onMock call and I don't have idea how mock this event and resolves to next then.

via Michał Niedziela