CBQE-2491: add tests for letting

Change-Id: Ieb0cefb95eb99c639fcf872be8973ef6642d715d
Reviewed-on: http://review.couchbase.org/43795
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>
Tested-by: buildbot <build@couchbase.com>