Add a unit test for utils.parsing
Add a unit test for utils.parsing

Most of the coverage comes from the main test suite, but this covers the
case where the lextab/parsetab does not yet exist and has to be
generated.

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