Adding ls command for tox

Author: ruaridhg

tox.ini

@@ -13,7 +13,9 @@ python =
 extras = testing
 allowlist_externals =
     cp
+    ls
 commands =
     cp -R {toxinidir}/src/napari_matplotlib/tests/baseline {envdir}/baseline
+    ls {toxinidir}/src/napari_matplotlib/tests/baseline
     python -c 'from skimage import data; data.brain()'
     python -m pytest --mpl -v --color=yes --cov=napari_matplotlib --cov-report=xml