I am unit testing a wrapper to the MongoDB C# driver. I have this line of code:
Collection.Find(predicate).ToListAsync();
Where Collection is of type IMongoCollection<T> and Find(predicate) returns an instance implementing IFindFluent<T, T>. ToListAsync() is an extension to turn the results into a list, I assume.
I am attempting to write unit tests, and I am stumped on handling this. I can't make a wrapper class because that's what I'm working on. I would prefer to either make it so ToListAsync() returns a created list OR to mock the Find() to return something that can be made a list of.
If anyone would struggle with getting it to work, what I did to mock Find() method was:
[TestFixture]
class QueryControllerTests
{
private IOptions<MongoSettings> _mongoSettings;
private QueryController _queryController;
private Mock<IFakeMongoCollection> _fakeMongoCollection;
private Mock<IFindFluent<BsonDocument, BsonDocument>> _fakeCollectionResult;
[OneTimeSetUp]
public void Setup()
{
_fakeMongoCollection = new Mock<IFakeMongoCollection>();
_fakeCollectionResult = new Mock<IFindFluent<BsonDocument, BsonDocument>>();
}
}
where IFakeMongoCollection is:
public interface IFakeMongoCollection : IMongoCollection<BsonDocument>
{
IFindFluent<BsonDocument, BsonDocument> Find(FilterDefinition<BsonDocument> filter, FindOptions options);
}
I wound up making a little abstraction layer for this, since I couldn't find anything suitable and asking for help yielded no answers.
I created an interface/implementation pair called AppCollection specifically to handle the MongoDB interface. IAppCollection would have a method for IAppCollection.ToList(predicate), and the AppCollection would run the Collection.Find(predicate).ToListAsync(); call, returning the list. Later, it was a trivial matter to mock the IAppCollection to make sure the right calls were being made. While I couldn't test the predicates in native LINQ, I could at least compile the predicates and compare them to passing/failing objects.