Unit testing with MongoDB

manpreet Best Answer 2 years ago

My database of choice is MongoDB. I'm writing a data-layer API to abstract implementation details from client applications - that is, I'm essentially providing a single public interface (an object which acts as an IDL).

I'm testing my logic as I go in a TDD manner. Before each unit test, an @Before method is called to create a database singleton, after which, when the test completes, an @After method is called to drop the database. This helps to promote independence among unit tests.

Nearly all unit tests, i.e. performing a contextual query, require some kind of insertion logic to occur before hand. My public interface provides an insert method - yet, it seems incorrect to use this method as precursor logic to each unit test.

Really I need some kind of mocking mechanism, yet, I haven't had much experience with mocking frameworks, and it seems that Google returns nothing re a mocking framework one might use with MongoDB.

What do others do in these situations? That is, how do people unit test code that interacts with a database?

Also, my public interface connects to a database defined in a external configuration file - it seems incorrect to use this connection for my unit testing - again, a situation that would benefit from some kind of mocking?

manpreet 2 years ago

Mongo mongo = PowerMockito.mock(Mongo.class);
DB db = PowerMockito.mock(DB.class);
DBCollection dbCollection = PowerMockito.mock(DBCollection.class);

PowerMockito.when(mongo.getDB("foo")).thenReturn(db);
PowerMockito.when(db.getCollection("bar")).thenReturn(dbCollection);

MyService svc = new MyService(mongo); // Use some kind of dependency injection
svc.getObjectById(1);

PowerMockito.verify(dbCollection).findOne(new BasicDBObject("_id", 1));