Instead of manually defining dev deps, use requirements-dev.

.drone.yml

@@ -19,7 +19,7 @@ steps:
     image: python:3.8
     commands:
       - python setup.py install
-      - pip install pytest coverage codecov
+      - pip install -r requirements-dev.txt
       - coverage run -m pytest
       - codecov -t $CODECOV_TOKEN
     environment:

requirements-dev.txt

@@ -3,3 +3,4 @@
 # dependencies for testing
 pytest>=3.2.5
 codecov>=1.4.0
+coverage==5.5