Fix config merge test for Jupyter Core 5.0 (#1068)

tests/extension/test_serverextension.py

@@ -1,6 +1,12 @@
 from collections import OrderedDict
 
 import pytest
+
+try:
+    from jupyter_core.paths import prefer_environment_over_user
+except ImportError:
+    prefer_environment_over_user = None
+
 from traitlets.tests.utils import check_help_all_output
 
 from jupyter_server.config_manager import BaseJSONConfigManager
@@ -43,6 +49,7 @@ def test_disable(jp_env_config_path, jp_extension_environ):
     assert not config["mock1"]
 
 
+@pytest.mark.skipif(prefer_environment_over_user is None, reason="Requires jupyter_core 5.0+")
 def test_merge_config(jp_env_config_path, jp_configurable_serverapp, jp_extension_environ):
     # Toggle each extension module with a JSON config file
     # at the sys-prefix config dir.
@@ -62,12 +69,12 @@ def test_merge_config(jp_env_config_path, jp_configurable_serverapp, jp_extensio
     # when these two configs merge.
     toggle_server_extension_python(
         "tests.extension.mockextensions.mockext_both",
-        enabled=True,
+        enabled=False,
         sys_prefix=True,
     )
     toggle_server_extension_python(
         "tests.extension.mockextensions.mockext_both",
-        enabled=False,
+        enabled=True,
         user=True,
     )
 
@@ -82,7 +89,8 @@ def test_merge_config(jp_env_config_path, jp_configurable_serverapp, jp_extensio
     assert extensions["tests.extension.mockextensions.mockext_sys"]
     assert extensions["tests.extension.mockextensions.mockext_py"]
     # Merging should causes this extension to be disabled.
-    assert not extensions["tests.extension.mockextensions.mockext_both"]
+    if prefer_environment_over_user():
+        assert not extensions["tests.extension.mockextensions.mockext_both"]
 
 
 @pytest.mark.parametrize(