add more test cases

Author: zacharyburnett

.github/workflows/test_tox.yml

@@ -83,10 +83,11 @@ jobs:
     uses: ./.github/workflows/tox.yml
     with:
       envs: |
+        - linux: pep8
         - linux: py3
       fill: true
-      fill_platforms: linux
-      fill_factors: xdist
+      fill_platforms: linux,macos
+      fill_factors: python_version
       pytest: false
 
   test_libraries: