add tests for Coordinate columns [skip ci]
add tests for Coordinate columns
[skip ci]

pllim/astropy,saimn/astropy,astropy/astropy,mhvk/astropy,lpsinger/astropy,larrybradley/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,lpsinger/astropy,pllim/astropy,astropy/astropy,saimn/astropy,lpsinger/astropy,StuartLittlefair/astropy,mhvk/astropy,mhvk/astropy,larrybradley/astropy,astropy/astropy,lpsinger/astropy,larrybradley/astropy,pllim/astropy,mhvk/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,larrybradley/astropy,saimn/astropy,mhvk/astropy,larrybradley/astropy,lpsinger/astropy,saimn/astropy,astropy/astropy,pllim/astropy,pllim/astropy,saimn/astropy,astropy/astropy