Add a simple test for the signature.x
Add a simple test for the signature.x

pllim/astropy,dhomeier/astropy,aleksandr-bakanov/astropy,lpsinger/astropy,mhvk/astropy,stargaser/astropy,aleksandr-bakanov/astropy,larrybradley/astropy,bsipocz/astropy,MSeifert04/astropy,mhvk/astropy,astropy/astropy,mhvk/astropy,StuartLittlefair/astropy,aleksandr-bakanov/astropy,dhomeier/astropy,astropy/astropy,StuartLittlefair/astropy,saimn/astropy,mhvk/astropy,astropy/astropy,lpsinger/astropy,stargaser/astropy,dhomeier/astropy,pllim/astropy,lpsinger/astropy,StuartLittlefair/astropy,larrybradley/astropy,StuartLittlefair/astropy,lpsinger/astropy,dhomeier/astropy,StuartLittlefair/astropy,larrybradley/astropy,dhomeier/astropy,larrybradley/astropy,saimn/astropy,stargaser/astropy,stargaser/astropy,bsipocz/astropy,saimn/astropy,MSeifert04/astropy,bsipocz/astropy,saimn/astropy,mhvk/astropy,MSeifert04/astropy,larrybradley/astropy,saimn/astropy,pllim/astropy,astropy/astropy,pllim/astropy,astropy/astropy,lpsinger/astropy,pllim/astropy,bsipocz/astropy,MSeifert04/astropy,aleksandr-bakanov/astropy