diff --git a/tests/test_nb_run.py b/tests/test_nb_run.py
index e263030..a5dfc61 100644
--- a/tests/test_nb_run.py
+++ b/tests/test_nb_run.py
@@ -8,7 +8,9 @@
 from nbmake.nb_result import NotebookResult
 from nbmake.nb_run import NotebookRun
 
-from .helper import failing_nb, passing_nb, write_nb
+from .helper import failing_nb, passing_nb, testdir2, write_nb
+
+assert testdir2  # ensure testdir is not removed by linter
 
 pytest_plugins = "pytester"
 
diff --git a/tests/test_pytest_plugin.py b/tests/test_pytest_plugin.py
index 232b7ff..0cd61b2 100644
--- a/tests/test_pytest_plugin.py
+++ b/tests/test_pytest_plugin.py
@@ -8,7 +8,9 @@
 from pytest import ExitCode, Pytester
 from typing_extensions import Never
 
-from .helper import failing_nb, passing_nb, write_nb
+from .helper import failing_nb, passing_nb, testdir2, write_nb
+
+assert testdir2  # ensure testdir is not removed by linter
 
 pytest_plugins = "pytester"
 NB_VERSION = 4