Using Sinon to stub chained Mongoose calls

If you use Promise, you can try sinon-as-promised:

sinon.stub(Mongoose.Model, 'findOne').returns({
  exec: sinon.stub().rejects(new Error('pants'))
  //exec: sinon.stub(). resolves(yourExepctedValue)
});

Take a look to sinon-mongoose. You can expects chained methods with just a few lines:

sinon.mock(YourModel).expects('findOne')
  .chain('where').withArgs('someBooleanProperty')
  .chain('exec')
  .yields(someError, someResult);

You can find working examples on the repo.

Also, a recommendation: use mock method instead of stub, that will check the method really exists.

I've solved it by doing the following:

var mockFindOne = {
    where: function () {
        return this;
    },
    equals: function () {
        return this;
    },
    exec: function (callback) {
        callback(null, "some fake expected return value");
    }
};

sinon.stub(mongoose.Model, "findOne").returns(mockFindOne);

Another way is to stub or spy the prototype functions of the created Query (using sinon):

const mongoose = require('mongoose');

sinon.spy(mongoose.Query.prototype, 'where');
sinon.spy(mongoose.Query.prototype, 'equals');
const query_result = [];
sinon.stub(mongoose.Query.prototype, 'exec').yieldsAsync(null, query_result);