How to make native node mongo return an err in callback

Question

I need to test error handling in a node app I'm working on. How can I make Mongo return an error in its callback so I can test error handling in my app?

collection.findOne({a: b}, function(err, item) {
   // how can I build a query to make an err?
});

Answer 1

One way I'm thinking is to use an invalid opereator:

collection.findOne({foo: {'$fooooo': true}}, function(err, item) {
  console.log(err);
});

prints:

{ [MongoError: invalid operator: $fooooo] name: 'MongoError' }

Answer 2

In your test, rather than requireing your actual Mongo driver, you could use a mock dummy driver that returns errors.

Answer 3

Running thisIsNotACollection.findOne({a:b}) in the CLI gives - ReferenceError: thisIsNotACollection is not defined. As long as you never define thisIsNotACollection as a collection you should consistently get an error back.