Chai/Sinon: How to spy on the return value of a promise returned by a function?

Question

I'm setting up unit + integration tests for onAfterDelete:

Assessment.onAfterDelete = async () => {
  ...

  // Log assessment deleted
  await Activity.create({
    assessmentId,
    activityTypeId: ACTIVITY_TYPE.ASSESSMENT_DELETED,
  }, options);

  ...
};

While I know how to test that Activity.create was called, I'd really like to test that the Activity was successfully created.

If it wasn't asynchronous, then I'd use Sinon.spy as follows:

it('logs the assessment deleted activity', async () => {
  sinon.spy(Activity, 'create');
  await Assessment.onAfterDelete(...);
  expect(Activity.create).returned({
    activityTypeId: ACTIVITY_TYPE.ASSESSMENT_DELETED,
    assessmentId: standardAssessmentData.id,
  });
  Activity.create.restore();
});

Of course, this doesn't work as Activity.create returns a Promise.

After an hour Googling the various flavors of Chai and Sinon with promises, I'm yet to find a solution to this use case. How can I test this return value?

Answer 1

You can use chai-as-promised:

const chai           = require('chai');
const chaiAsPromised = require('chai-as-promised');
chai.use(chaiAsPromised);

it('logs the assessment deleted activity', async () => {
  sinon.spy(Activity, 'create');
  await Assessment.onAfterDelete();

  // Make sure `Activity.create()` got called.
  expect(Activity.create.called).to.be.true;

  // Check the resolved value.
  await expect(Activity.create.firstCall.returnValue).to.eventually.equal({
    activityTypeId : ACTIVITY_TYPE.ASSESSMENT_DELETED,
    assessmentId   : standardAssessmentData.id,
  });

  // Restore the original.
  Activity.create.restore();
});