The following integration tests have been failing when run against the inMemory storage engine on the 6.0 branch ever since the changes from SERVER-70395 were backported to 6.0:

• jstests/aggregation/spill_to_disk.js
• jstests/noPassthrough/spill_to_disk_secondary_read.js

They are failing essentially because of SERVER-73757. That is, the inMemory storage engine reports the storage size of a TemporaryRecordStore used for spilling as 0. This causes assertions about the spilledDataStorageSize to fail. The only reason that we don't see a similar failure on the master branch is that the tests in question were tagged with "requires_persistence" as part of the work for SERVER-70493. This prevents them from running against the inMemory storage engine. We should solve the problem on the 6.0 by adding the missing "requires_persistence" tags.

As a side note: related ticket SERVER-73717 may also be of interest since it proposes a potential change for how spilling to a TemporaryRecordStore works with the inMemory storage engine.