Rely on pytest-enabler to enable pytest-xdist when present and enabled.

pyproject.toml

@@ -24,6 +24,9 @@ addopts = "--flake8"
 [pytest.enabler.cov]
 addopts = "--cov"
 
+[pytest.enabler.xdist]
+addopts = "-n auto"
+
 [tool.towncrier]
     package = "setuptools"
     package_dir = "setuptools"

pytest.ini

@@ -4,9 +4,6 @@ addopts=
 	--doctest-modules
 	--doctest-glob=pkg_resources/api_tests.txt
 	-r sxX
-
-	# `pytest-xdist`:
-	-n auto
 doctest_optionflags=ALLOW_UNICODE ELLIPSIS
 # workaround for warning pytest-dev/pytest#6178
 junit_family=xunit2

setup.cfg

@@ -47,7 +47,7 @@ testing =
 	pytest-black >= 0.3.7; python_implementation != "PyPy"
 	pytest-cov
 	pytest-mypy; python_implementation != "PyPy"
-	pytest-enabler
+	pytest-enabler >= 1.0.1
 
 	# local
     mock