Define and use a [tests] extra

Author: hroncok

setup.py

@@ -22,6 +22,13 @@ def long_description():
         "tox>=3.15,<4",
         "importlib_metadata; python_version < '3.8'"
     ],
+    extras_require={
+        "tests": [
+            "pytest",
+            "pytest-xdist",
+            "packaging",
+        ],
+    },
     python_requires=">=3.6",
     classifiers=[
         "Development Status :: 3 - Alpha",

tox.ini

@@ -5,10 +5,9 @@
 envlist = {py36,py37,py38,py39,py310}-tox{release,master,315}
 
 [testenv]
+extras =
+    tests
 deps=
-    pytest
-    pytest-xdist
-    packaging
     tox315: tox >=3.15,<3.16
     toxrelease: tox < 4
     toxmaster: git+https://github.com/tox-dev/tox.git@master