added pytest-cov to github actions config

.github/workflows/tests.yml

@@ -24,7 +24,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          python -m pip install flake8 pytest
+          python -m pip install flake8 pytest pytest-cov pylint 
           if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
       - name: Lint with flake8
         run: |