diff --git a/tests/conftest.py b/tests/conftest.py
index bcfc91f1345ed..745ec9f4178b3 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -25,6 +25,7 @@
 
 # We should set these before loading _any_ of the rest of airflow so that the
 # unit test mode config is set as early as possible.
+assert "airflow" not in sys.modules, "No airflow module can be imported before these lines"
 tests_directory = os.path.dirname(os.path.realpath(__file__))
 
 os.environ["AIRFLOW__CORE__DAGS_FOLDER"] = os.path.join(tests_directory, "dags")