Test style in CI (but don't fail)

.gitlab-ci.yml

 image: python:3.7
 
+stages:
+  - test
+  - formatting
+  - deploy
+
 test:
   stage: test
   tags: ["docker"]
@@ -7,6 +12,19 @@ test:
     - pip install -e ".[testing]" -i https://iweb1.sips/eggs --trusted-host iweb1.sips
     - py.test -xv
 
+formatting:
+    stage: formatting
+    tags:
+        - docker
+    allow_failure: true
+    only:
+        - branches
+    except:
+        - master
+    script:
+        - pip install black
+        - black --diff --check edosl0util
+
 sdist:
   stage: deploy
   only: