Run pytest on commit

.gitlab-ci.yml

+stages:
+  - test
+  - deploy
+
+cache:
+  paths:
+    - ~/.cache/pip/
+
+.test: &test_template
+  stage: test
+  before_script:
+    - pip3 install .
+  script:
+    - python3 -m pytest
+
+test:PY3.7:
+  <<: *test_template
+  image: python:3.7
+
+test:PY3.8:
+  <<: *test_template
+  image: python:3.8
+
+test:PY3.9:
+  <<: *test_template
+  image: python:3.9
+
 build-package:
   stage: deploy
-  image: python:3
+  image: python:3.7
   script:
     - cat $PYPIRC > /tmp/.pypirc
     - pip3 install twine