If clients created with disableClientPersistence=true are not explicitly freed after a test, they may accumulate and not get freed until the end of the test suite (not just test case). This is relevant if the clients or any object that references them are assigned to a class property in the test case and not explicitly unset during tearDown().

It's not clear why references to the Manager object are being maintained, so we should look into this.

This came up in mongodb/mongo-php-library#1064.