In https://jira.mongodb.org/browse/RUBY-2165 the block form of the Client constructor was fixed to close the client after the block finished and tests were added asserting that the client's cluster is closed after block finishes.

Besides cluster, a client also creates an auto encrypter which may create its own client. It may be useful to extend the tests to also assert that the encrypter's client is closed when block form is used.