Mocking / stubbing mongoose findById with sinon
Take a look to sinon-mongoose. You can expects chained methods with just a few lines:
// If you are using callbacks, use yields so your callback will be calledsinon.mock(YourModel) .expects('findById').withArgs('abc123') .chain('exec') .yields(someError, someResult);// If you are using Promises, use 'resolves' (using sinon-as-promised npm) sinon.mock(YourModel) .expects('findById').withArgs('abc123') .chain('exec') .resolves(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.
Since it seems you are testing a single class, I'd roll with the generic
var mongoose = require('mongoose');var accountStub = sinon.stub(mongoose.Model, 'findById');This will stub any calls to Model.findById patched by mongoose.