JCBC-332 : Tests added for observe and arithmetic operations

Change-Id: Ie6bfac06cf168fddbbd7808a2579ece1e080c700
Reviewed-on: http://review.couchbase.org/27610
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Deepti Dawar <deepti.dawar@globallogic.com>