public void TestDistinct()
{
_collection.RemoveAll();
_collection.DropAllIndexes();
_collection.Insert(new BsonDocument("x", 1));
_collection.Insert(new BsonDocument("x", 2));
_collection.Insert(new BsonDocument("x", 3));
_collection.Insert(new BsonDocument("x", 3));
var values = new HashSet<BsonValue>(_collection.Distinct("x"));
Assert.AreEqual(3, values.Count);
Assert.AreEqual(true, values.Contains(1));
Assert.AreEqual(true, values.Contains(2));
Assert.AreEqual(true, values.Contains(3));
Assert.AreEqual(false, values.Contains(4));
}