add tox dep

Author: Matt Sokoloff

.github/workflows/python-package.yml

@@ -59,7 +59,6 @@ jobs:
     - name: Install package and test dependencies
       run: |
         pip install tox==3.18.1
-        pip install pytest-cases
 
     # TODO: replace tox.ini with what the Makefile does
     # to make sure local testing is

tox.ini

@@ -7,5 +7,6 @@ envlist = py36, py37, py38
 deps =
     -rrequirements.txt
     pytest
+    pytest-cases
 passenv = LABELBOX_TEST_API_KEY_PROD LABELBOX_TEST_API_KEY_STAGING LABELBOX_TEST_ENVIRON
 commands = pytest {posargs}