Add test that checks we cannot overwrite read or write
Add test that checks we cannot overwrite read or write

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