TST: update mgrid test from code review
TST: update mgrid test from code review

Co-authored-by: Ross Barnowski <e9fb290bfd0a4406872fd6103425d9efafcfa051@berkeley.edu>
seberg/numpy,pbrod/numpy,pbrod/numpy,mhvk/numpy,rgommers/numpy,endolith/numpy,simongibbons/numpy,grlee77/numpy,anntzer/numpy,mhvk/numpy,jakirkham/numpy,pdebuyl/numpy,mattip/numpy,seberg/numpy,grlee77/numpy,jakirkham/numpy,madphysicist/numpy,charris/numpy,madphysicist/numpy,mattip/numpy,endolith/numpy,pbrod/numpy,rgommers/numpy,seberg/numpy,charris/numpy,simongibbons/numpy,pbrod/numpy,madphysicist/numpy,mattip/numpy,rgommers/numpy,jakirkham/numpy,madphysicist/numpy,pbrod/numpy,anntzer/numpy,simongibbons/numpy,mhvk/numpy,grlee77/numpy,charris/numpy,mhvk/numpy,pdebuyl/numpy,numpy/numpy,anntzer/numpy,pdebuyl/numpy,numpy/numpy,grlee77/numpy,simongibbons/numpy,endolith/numpy,jakirkham/numpy,anntzer/numpy,mattip/numpy,jakirkham/numpy,endolith/numpy,simongibbons/numpy,mhvk/numpy,numpy/numpy,rgommers/numpy,pdebuyl/numpy,grlee77/numpy,numpy/numpy,charris/numpy,madphysicist/numpy,seberg/numpy