[Madoshakalaka#75] add tox job

Signed-off-by: Bryant Finney <finneybp@gmail.com>

.gitlab/ci/main.yml

@@ -10,20 +10,26 @@ workflow:
       when: never
     - when: always
 
+.parallel python versions:
+  # jobs that extend this one are executed in parallel
+  parallel:
+    matrix:
+      - PY_MAJOR: 3
+        PY_MINOR: [6, 7, 8]
+
 update python images:
+  # when the pipeline is executed on a schedule / manually, update the Docker images
+  # in the project registry
   after_script: [docker logout $CI_REGISTRY]
 
   before_script:
     - docker login $CI_REGISTRY -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD
 
+  extends: [.parallel python versions]
+
   image: docker:20.10
   needs: []
 
-  parallel:
-    matrix:
-      - PY_MAJOR: 3
-        PY_MINOR: [6, 7, 8]
-
   rules:
     - if: $CI_PIPELINE_SOURCE == "web"
     - if: $CI_PIPELINE_SOURCE == "schedule"
@@ -37,3 +43,14 @@ update python images:
   stage: build
   variables:
     DOCKER_IMAGE: python:${PY_MAJOR}.${PY_MINOR}
+
+tox:
+  # use tox to run the test suite in the python image
+  before_script: [pip3 install --upgrade tox]
+  extends: [.parallel python versions]
+  image: $CI_REGISTRY_IMAGE/python:${PY_MAJOR}.${PY_MINOR}
+
+  needs: []
+  script:
+    - tox -e py${PY_MAJOR}${PY_MINOR} .
+  stage: test