Resolve CWG-11 "Features/ add tox"

Closes CWG-11

.gitlab-ci.yml

 default:
-  image: python:3.7 # minimum supported version
+  image: python:3.10  # use latest for building/linting
   before_script:
     - python --version # For debugging
     - python -m pip install --upgrade pip
@@ -47,8 +47,12 @@ run_pylint:
 
 run_unit_tests:
   stage: test
+  image: python:3.${PY_VERSION}
   script:
-    - tox -e py37,py38,py39,py310
+    - tox -e py3${PY_VERSION}
+  parallel:
+    matrix: # use the matrix for testing
+      - PY_VERSION: [7, 8, 9, 10]
 
 package_files:
   stage: package