Show deprecation message when running under Python 2.7 and 3.4

Fix #4627

testing/deprecated_test.py

@@ -3,6 +3,7 @@ from __future__ import division
 from __future__ import print_function
 
 import os
+import sys
 
 import pytest
 from _pytest.warnings import SHOW_PYTEST_WARNINGS_ARG
@@ -219,3 +220,21 @@ def test_fixture_named_request(testdir):
             "*'request' is a reserved name for fixtures and will raise an error in future versions"
         ]
     )
+
+
+def test_python_deprecation(testdir):
+    result = testdir.runpytest()
+    python_ver = ".".join(str(x) for x in sys.version_info[:3])
+    msg = "You are using Python {}, which will no longer be supported in pytest 5.0".format(
+        python_ver
+    )
+    if sys.version_info[:2] <= (3, 4):
+        result.stdout.fnmatch_lines(
+            [
+                msg,
+                "For more information, please read:",
+                "  https://docs.pytest.org/en/latest/py27-py34-deprecation.html",
+            ]
+        )
+    else:
+        assert msg not in result.stdout.str()