diff --git a/tests/test_platform.py b/tests/test_platform.py
index 9ae1f07..123181d 100644
--- a/tests/test_platform.py
+++ b/tests/test_platform.py
@@ -47,6 +47,10 @@ def setUp(self):
             self.assertTrue(os.path.isdir(self.dir))
 
     def _collect_shared(self, name):
+        # stdlib extensions are not in subdirectories
+        if '/' in name:
+            return None
+
         return name.split('.', 1)[0]
 
     def _collect_file(self, name):