Use Case

As a... user with an unset minPoolSize and set maxIdleTimeMS
I want... perished connections to be periodically cleaned up in the background
So that...  I don't leave unusable resources open while the pool is idle

User Experience

• Improvement, follow-up from NODE-6580

Unknowns

• Should we update the background thread frequency to be configurable?

Acceptance Criteria

Implementation Requirements

• Change the condition in the background thread that ensures that minPoolSize is being followed, to ensure that when minPoolSize = 0, perished connections are still appropriately purged
• See background thread CMAP spec here: https://github.com/mongodb/specifications/blob/master/source/connection-monitoring-and-pooling/connection-monitoring-and-pooling.md#background-thread

Testing Requirements

• Add a test to make sure that the cleanup happens (make sure it fails before the fix and succeeds after)

Documentation Requirements

• Update API docs for maxIdleTimeMS to reflect spec documentation and also clarify the difference between being 'idle' / or unused and being marked as 'idle'

Follow Up Requirements

• N/A