timeseries_group_aggregation.js has a hard coded mention to the system buckets namespace here. I tried to change this quickly in SERVER–14625 to use the viewless timeseries helper, but my change caused the test to time out in burn_in suites. We should use this ticket to investigate why this is happening in this test.

Note: there are tests that are able to get the plan cache with viewless timeseries (example).