Testing: run Coverage report only on CircleCI (#10611)

* Testing: run Coverage report only on CircleCI due to Python debugger

I've been hitting an issue while debugging test cases that it doesn't stop
exactly where I put the breakpoint. This has been pretty annoying since I'm in
the middle of an inner function and I have to do multiple steps forward to find
the exact place where I put my breakpoint.

Today I found this problem is due to an incompatibility of `pytest-cov` and the
debuggers: https://pytest-cov.readthedocs.io/en/latest/debuggers.html.

* Declare the variable in the Python Docker container

Author: humitos

.circleci/config.yml

@@ -10,6 +10,7 @@ jobs:
       - image: 'cimg/python:3.10'
         environment:
           TOX_POSARGS: ''
+          PYTEST_COVERAGE: --cov-report=xml --cov-config .coveragerc --cov=. --cov-append
       - image: 'docker.elastic.co/elasticsearch/elasticsearch:7.14.0'
         name: search
         environment:

tox.ini

@@ -16,14 +16,16 @@ deps =
   -r requirements/testing.txt
 basepython =
     python3.10
+# https://pytest-cov.readthedocs.io/en/latest/debuggers.html
+# https://github.com/microsoft/vscode-python/issues/693
 commands =
     sh -c '\
         export DJANGO_SETTINGS_MODULE=readthedocs.settings.test; \
-        pytest --cov-report=xml --cov-config .coveragerc --cov=. --pyargs readthedocs --suppress-no-test-exit-code -m "not proxito and not embed_api" {posargs:{env:TOX_POSARGS:-m "not search and not proxito and not embed_api"}}'
+        pytest {env:PYTEST_COVERAGE} --pyargs readthedocs --suppress-no-test-exit-code -m "not proxito and not embed_api" {posargs:{env:TOX_POSARGS:-m "not search and not proxito and not embed_api"}}'
 
     sh -c '\
         export DJANGO_SETTINGS_MODULE=readthedocs.settings.proxito.test; \
-        pytest --cov-report=xml --cov-config .coveragerc --cov=. --cov-append --pyargs readthedocs -m proxito --suppress-no-test-exit-code {posargs}'
+        pytest {env:PYTEST_COVERAGE} --pyargs readthedocs -m proxito --suppress-no-test-exit-code {posargs}'
 allowlist_externals =
     sh
     git