db.dropDatabase(); const pipeline = [ { "$densify" : { "field" : "num" , "partitionByFields" : [ "key" ], "range" : { "step" : 1, "bounds" : [ 4, 8 ] } }}, {$sort: { num: 1}}, {$project: { _id: 0, num: 1 }} ]; // Expected result set is [4,5,6,7]. assert .eq(4, db.collection.aggregate(pipeline).itcount()); db.collection.insertMany([ { "key" : 1, "num" : 2}, { "key" : 1, "num" : 4}, { "key" : 1, "num" : 6} ]); // Expected result set is [2,4,5,6,7]. Fails assert with a result set of [2,3,4,4,5,6,7]. assert .eq(5, db.collection.aggregate(pipeline).itcount());