Print warning when running setup.py test

setup.py

@@ -3,6 +3,7 @@
 import os
 
 from setuptools import setup, find_packages
+from setuptools.command.test import test as TestCommand
 
 from dateutil._version import VERSION
 
@@ -11,6 +12,13 @@
 
 PACKAGES = find_packages(where='.', exclude=['dateutil.test'])
 
+
+class Unsupported(TestCommand):
+    def run(self):
+        print("Running 'test' with setup.py is not supported. "
+              "Use 'pytest' or 'tox' to run the tests.")
+
+
 setup(name="python-dateutil",
       version=VERSION,
       description="Extensions to the standard Python datetime module",
@@ -44,5 +52,8 @@
           'Programming Language :: Python :: 3.6',
           'Topic :: Software Development :: Libraries',
       ],
-      test_suite="dateutil.test"
+      test_suite="dateutil.test",
+      cmdclass={
+          "test": Unsupported
+      }
       )