TST: don't look in user site for serverextensions (#6233)

* TST: don't look in user site for serverextensions

Author: bnavigator

notebook/tests/test_serverextensions.py

@@ -1,5 +1,6 @@
 import imp
 import os
+import site
 import sys
 from unittest import TestCase
 from unittest.mock import patch
@@ -84,6 +85,11 @@ def setUp(self):
             p = patch.object(mod,
                 'ENV_CONFIG_PATH', [])
             self.patches.append(p)
+        # avoid adding the user site to the config paths with jupyter-core >= 4.9
+        # https://github.com/jupyter/jupyter_core/pull/242
+        p = patch.object(site,
+            'ENABLE_USER_SITE', False)
+        self.patches.append(p)
         for p in self.patches:
             p.start()
             self.addCleanup(p.stop)