Add a unit test for thread safety of lazy classproperty
Add a unit test for thread safety of lazy classproperty

astropy/astropy,mhvk/astropy,pllim/astropy,mhvk/astropy,mhvk/astropy,lpsinger/astropy,aleksandr-bakanov/astropy,lpsinger/astropy,dhomeier/astropy,StuartLittlefair/astropy,saimn/astropy,StuartLittlefair/astropy,dhomeier/astropy,StuartLittlefair/astropy,larrybradley/astropy,dhomeier/astropy,dhomeier/astropy,larrybradley/astropy,astropy/astropy,saimn/astropy,pllim/astropy,astropy/astropy,aleksandr-bakanov/astropy,astropy/astropy,saimn/astropy,StuartLittlefair/astropy,dhomeier/astropy,pllim/astropy,lpsinger/astropy,larrybradley/astropy,saimn/astropy,StuartLittlefair/astropy,mhvk/astropy,lpsinger/astropy,lpsinger/astropy,pllim/astropy,aleksandr-bakanov/astropy,aleksandr-bakanov/astropy,pllim/astropy,saimn/astropy,larrybradley/astropy,astropy/astropy,mhvk/astropy,larrybradley/astropy