Testing a callback nested in a promise

Question

tl;dr I need to test that my method adds a row to a spreadsheet on successful load of a Google spreadsheet.

saveDataToGoogleSpreadSheet(conversationData){
  return new Promise((resolve, reject) => {
    Spreadsheet.load(this.getGoogleAPISettings(), (err, spreadsheet) => {
      if (err) {
        return reject(err);
      }

      return spreadsheet.receive((receivedError, rows, info) => {
        if (receivedError) {
          return reject(receivedError);
        }
        const rowData = this.getSpreadsheetRowData(conversationData, info.totalRows);
        spreadsheet.add(rowData);
        return spreadsheet.send(sendError => (sendError ? reject(sendError) : resolve()));
      });
    });
  });
}

I tested the case one and case two of the function (the two first errors) but I couldn't do it for the last one, the case of success where we an add a row to a spreadsheet.

I need some help with the structure of the test, or a hint on how could my test be.

Edit: how the previous tests were made

it('should add a row to a Google Spreadsheet', (done) => {
      nock('https://spreadsheets.google.com')
      .post('/feeds/cells/1ZOd7Sysc-JNa-D5AHb7ZJkwBRMBGaeKpzIwEl7B8RbQ/1/private/full/batch')
      .replyWithError({ message: 'abcde' });
      api.saveDataToGoogleSpreadSheet({ data: 'some data' })
      .then(() => done(new Error('should not have made the call')))
      .catch((err) => {
        expect(err).to.equal('Error Reading Spreadsheet');
        done();
      });
    }).timeout(4000);

Answer 1

It is hard to tell what is the problem with the test from the little code you have, and no background on what the various objects are and how they come to be, so I will just assume that Spreadsheet is an object that is created through a library you require, and other than that, all other objects are created by the module. i.e. I assume you somewhere have a line resembling something like this:

const Spreadsheet = require('some-google-docs-spreadsheet-lib');

That means one problem is finding out how to control the Spreadsheet object so we can stub out its behavior.

Just to start you out, you might get some good pointers on general code and test structure for easy testing from these two answers, as they cover the two most relevant techniques: dependency injection and exploiting link seams.

• Mocking Redis Constructor with Sinon
• How to test an ES6 class that needs jquery?

For all I know, you might already utilize one of these techniques, as you say you have been able to test the two error situations. But maybe you have not really been unit testing and done the actual network calls to the service instead (which is more of an integration test)? Anyway, I'll assume no more than what I wrote above and show you how to do the testing using proxyquire:

const assert = require('assert');
const dummy = ()=> {};
const SpreadSheetStubLibrary = { load: dummy };
const MyClassToTest = proxyquire('../src/my-module', { 
    'some-google-docs-spreadsheet-lib': SpreadSheetStubLibrary
})
const config = {};
const conversationData = {};

let stubSetup;
let spreadsheet;
let myObj;

function setupStubs() {
    stubSetup = stubSpreadsheetLoadFunction();
    spreadsheet = stubSetup.spreadsheet;
    SpreadSheetStubLibrary.load = stubSetup.load;

    myObj = new MyClassToTest(config);
    conversationData = {};
};

function createSpreadsheetStubObj(){
    return {
        receive: sinon.stub(),
        add: sinon.stub(),
        send: sinon.stub()
    }
}

function stubSpreadsheetLoadFunction(){
    const spreadsheet = createSpreadsheetStubObj();

    return { 
        load: (settings, cb) => cb(null, spreadsheet),
        spreadSheetStubObj: spreadsheet
    };
}


it('should add a row to the spreadsheet on successful load', () => {
    // Arrange
    setupStubs();
    const rowData = { foo: 1, bar: 2};
    spreadsheet.receive.yields(); // calls any callback given
    myObj.getSpreadsheetRowData = () => rowData; // see lines below

    // if you want to use the real getSpreadsheetRowData, uncomment these lines
    //const rows = []; // not used in the method?
    //const info = { totalRows : 100 };
    //spreadsheet.receive.yields(null, rows, info);

    // Act
    return myObj.saveDataToGoogleSpreadSheet(conversationData).then(()=>{
        // Assert
        assert(spreadsheet.add.calledOnce);
        assert(spreadsheet.add.calledWith(rowData));
    });
});


it('should add a row to the spreadsheet on successful load', () => {
    // reuse the above
});

See the Sinon docs for the stub API.

Disclosure: I am part of the Sinon maintainer team.