Reorganize test requirements

- Move test requirements from tox.ini to a test extra
- Removes unused test requirements
- Pin-down incompatible pytest-xdist<2.0.0 due to
  pytest-dev/pytest-cov#422
- Bumps test requirements to decrease change of running outdated
  version while developing.

setup.cfg

@@ -77,6 +77,16 @@ install_requires =
   # NOTE: per issue #509 0.15.34 included in debian backports
   typing-extensions; python_version < "3.8"
 
+[options.extras_require]
+test =
+  pytest >= 6.0.1
+  pytest-cov >= 2.10.0
+  # https://github.com/pytest-dev/pytest-cov/issues/422
+  pytest-xdist >= 1.34.0,<2.0.0
+  # Needed to avoid DeprecationWarning errors in pytest:
+  setuptools >= 40.4.3
+  wheel >= 0.35.0
+
 [options.entry_points]
 console_scripts =
   ansible-lint = ansiblelint.__main__:main

tox.ini

@@ -20,15 +20,8 @@ deps =
   # https://github.com/ansible/ansible/issues/70705
   ansibledevel: ansible>=2.10.0a1,<2.11
   ansibledevel: ansible-base @ git+https://github.com/ansible/ansible.git
-  ruamel.yaml==0.16.5  # NOTE: 0.15.34 has issues with py37
-  flake8
-  pep8-naming
-  pytest
-  pytest-cov
-  pytest-xdist
-  # Needed to avoid DeprecationWarning errors in pytest:
-  setuptools >= 40.4.3
-  wheel
+extras =
+  test
 commands =
   # safety measure to assure we do not accidentaly run tests with broken dependencies
   python -m pip check