BUG/TEST: core: Fix an undefined name in a test.
BUG/TEST: core: Fix an undefined name in a test.

This hasn't generated an error because the test is marked `xfail`.
Code checkers such as pyflakes will flag it, so fixing it is worthwhile.

numpy/numpy,simongibbons/numpy,seberg/numpy,rgommers/numpy,charris/numpy,pdebuyl/numpy,madphysicist/numpy,jakirkham/numpy,simongibbons/numpy,pdebuyl/numpy,simongibbons/numpy,grlee77/numpy,abalkin/numpy,abalkin/numpy,mattip/numpy,charris/numpy,pbrod/numpy,simongibbons/numpy,seberg/numpy,pdebuyl/numpy,endolith/numpy,mattip/numpy,pbrod/numpy,madphysicist/numpy,WarrenWeckesser/numpy,charris/numpy,anntzer/numpy,rgommers/numpy,numpy/numpy,grlee77/numpy,madphysicist/numpy,WarrenWeckesser/numpy,mhvk/numpy,mhvk/numpy,jakirkham/numpy,endolith/numpy,numpy/numpy,WarrenWeckesser/numpy,endolith/numpy,charris/numpy,pbrod/numpy,mattip/numpy,anntzer/numpy,anntzer/numpy,rgommers/numpy,seberg/numpy,endolith/numpy,mhvk/numpy,rgommers/numpy,WarrenWeckesser/numpy,mhvk/numpy,grlee77/numpy,mhvk/numpy,jakirkham/numpy,abalkin/numpy,pbrod/numpy,pbrod/numpy,jakirkham/numpy,grlee77/numpy,anntzer/numpy,jakirkham/numpy,madphysicist/numpy,simongibbons/numpy,pdebuyl/numpy,seberg/numpy,madphysicist/numpy,numpy/numpy,WarrenWeckesser/numpy,mattip/numpy,grlee77/numpy