all_collection_stats.js is a test for the new aggregation pipeline stage  _internalAllCollectionStats that reports the statistics of all collections.
However, the test simply compares the json result of _internalAllCollectionStats with calling multiple times $collStats.

The result should be theoretically equivalent, unfortunately this test might fail since the collection stats contains some cache information that apparently can change among successive calls.

My suggestion is to simply compare some selected fields. However, any other solution is welcomed.