diff --git a/jupyter_server/tests/extension/test_app.py b/jupyter_server/tests/extension/test_app.py
index 1f262560ef..58fa38cda2 100644
--- a/jupyter_server/tests/extension/test_app.py
+++ b/jupyter_server/tests/extension/test_app.py
@@ -99,7 +99,7 @@ def test_stop_extension(jp_serverapp, caplog):
 
     # load extensions (make sure we only have the one extension loaded
     jp_serverapp.extension_manager.load_all_extensions()
-    extension_name = 'jupyter_server.tests.extension.mockextensions'
+    extension_name = "jupyter_server.tests.extension.mockextensions"
     assert list(jp_serverapp.extension_manager.extension_apps) == [extension_name]
 
     # add a stop_extension method for the extension app
diff --git a/jupyter_server/tests/extension/test_manager.py b/jupyter_server/tests/extension/test_manager.py
index 2b76af33cd..148b6ea6d9 100644
--- a/jupyter_server/tests/extension/test_manager.py
+++ b/jupyter_server/tests/extension/test_manager.py
@@ -1,4 +1,5 @@
 import os
+import unittest.mock as mock
 
 import pytest
 from jupyter_core.paths import jupyter_config_path
@@ -78,7 +79,7 @@ def test_extension_manager_api(jp_serverapp):
     jpserver_extensions = {"jupyter_server.tests.extension.mockextensions": True}
     manager = ExtensionManager(serverapp=jp_serverapp)
     assert manager.config_manager
-    expected = _normalize_path(os.path.join(jupyter_config_path()[0], 'serverconfig'))
+    expected = _normalize_path(os.path.join(jupyter_config_path()[0], "serverconfig"))
     assert _normalize_path(manager.config_manager.read_config_path[0]) == expected
     manager.from_jpserver_extensions(jpserver_extensions)
     assert len(manager.extensions) == 1
@@ -91,3 +92,41 @@ def test_extension_manager_linked_extensions(jp_serverapp):
     manager.add_extension(name, enabled=True)
     manager.link_extension(name)
     assert name in manager.linked_extensions
+
+
+def test_extension_manager_fail_add(jp_serverapp):
+    name = "jupyter_server.tests.extension.notanextension"
+    manager = ExtensionManager(serverapp=jp_serverapp)
+    manager.add_extension(name, enabled=True)  # should only warn
+    jp_serverapp.reraise_server_extension_failures = True
+    with pytest.raises(ExtensionModuleNotFound):
+        manager.add_extension(name, enabled=True)
+
+
+def test_extension_manager_fail_link(jp_serverapp):
+    name = "jupyter_server.tests.extension.mockextensions.app"
+    with mock.patch(
+        "jupyter_server.tests.extension.mockextensions.app.MockExtensionApp.parse_command_line",
+        side_effect=RuntimeError,
+    ):
+        manager = ExtensionManager(serverapp=jp_serverapp)
+        manager.add_extension(name, enabled=True)
+        manager.link_extension(name)  # should only warn
+        jp_serverapp.reraise_server_extension_failures = True
+        with pytest.raises(RuntimeError):
+            manager.link_extension(name)
+
+
+def test_extension_manager_fail_load(jp_serverapp):
+    name = "jupyter_server.tests.extension.mockextensions.app"
+    with mock.patch(
+        "jupyter_server.tests.extension.mockextensions.app.MockExtensionApp.initialize_handlers",
+        side_effect=RuntimeError,
+    ):
+        manager = ExtensionManager(serverapp=jp_serverapp)
+        manager.add_extension(name, enabled=True)
+        manager.link_extension(name)
+        manager.load_extension(name)  # should only warn
+        jp_serverapp.reraise_server_extension_failures = True
+        with pytest.raises(RuntimeError):
+            manager.load_extension(name)
diff --git a/jupyter_server/tests/services/kernels/test_cull.py b/jupyter_server/tests/services/kernels/test_cull.py
index 029ea0ba57..ad61b55ba4 100644
--- a/jupyter_server/tests/services/kernels/test_cull.py
+++ b/jupyter_server/tests/services/kernels/test_cull.py
@@ -15,7 +15,7 @@ def jp_argv(request):
     ]
 
 
-CULL_TIMEOUT = 10 if platform.python_implementation() == "PyPy" else 5
+CULL_TIMEOUT = 30 if platform.python_implementation() == "PyPy" else 5
 CULL_INTERVAL = 1
 
 
diff --git a/jupyter_server/tests/test_terminal.py b/jupyter_server/tests/test_terminal.py
index 0f41ece269..78da12b423 100644
--- a/jupyter_server/tests/test_terminal.py
+++ b/jupyter_server/tests/test_terminal.py
@@ -28,7 +28,7 @@ def terminal_path(tmp_path):
     shutil.rmtree(str(subdir), ignore_errors=True)
 
 
-CULL_TIMEOUT = 2
+CULL_TIMEOUT = 10
 CULL_INTERVAL = 3
 
 
@@ -128,7 +128,7 @@ async def test_terminal_create_with_cwd(jp_fetch, jp_ws_fetch, terminal_path):
     message_stdout = ""
     while True:
         try:
-            message = await asyncio.wait_for(ws.read_message(), timeout=1.0)
+            message = await asyncio.wait_for(ws.read_message(), timeout=5.0)
         except asyncio.TimeoutError:
             break
 
@@ -164,7 +164,7 @@ async def test_culling(jp_server_config, jp_fetch):
     last_activity = term["last_activity"]
 
     culled = False
-    for i in range(10):  # Culling should occur in a few seconds
+    for i in range(CULL_TIMEOUT + CULL_INTERVAL):
         try:
             resp = await jp_fetch(
                 "api",