tox.ini: passenv = PYYAML_TEST_GROUP
diff --git a/tox.ini b/tox.ini
index 8d1e42d..867f125 100644
--- a/tox.ini
+++ b/tox.ini
@@ -6,3 +6,4 @@
     Cython
 commands =
     python setup.py test
+passenv = PYYAML_TEST_GROUP