xfail for test_post_chunked_binary_secure on CPython 3.5

tests/integration/test_requests.py

@@ -1,6 +1,8 @@
 # -*- coding: utf-8 -*-
 '''Test requests' interaction with vcr'''
+import platform
 import pytest
+import sys
 import vcr
 from assertions import assert_cassette_empty, assert_is_json
 
@@ -115,6 +117,9 @@ def test_post_chunked_binary(tmpdir, httpbin):
 
 
 @pytest.mark.xfail('sys.version_info >= (3, 6)', strict=True, raises=ConnectionError)
+@pytest.mark.xfail((3, 5) < sys.version_info < (3, 6) and
+                   platform.python_implementation() == 'CPython',
+                   reason='Fails on CPython 3.5')
 def test_post_chunked_binary_secure(tmpdir, httpbin_secure):
     '''Ensure that we can send chunked binary without breaking while trying to concatenate bytes with str.'''
     data1 = iter([b'data', b'to', b'send'])