added also pytest-cov

requirements.txt

@@ -16,6 +16,7 @@ partd==1.2.0
 psutil==5.8.0
 pydot==1.4.2
 pytest==6.2.2
+pytest-cov==2.11.1
 pytest-html==3.1.1
 pytest-lazy-fixture==0.6.3
 requests==2.25.1