diff --git a/csst_proto/some_other_modules.py b/csst_proto/some_other_modules.py
index 426f56e4ad8d964a26684f94d46463606c07e1a3..3c73225d68c895e49383f3ff5eb65e93a11b1dbd 100644
--- a/csst_proto/some_other_modules.py
+++ b/csst_proto/some_other_modules.py
@@ -1,5 +1,3 @@
-def an_arbitrary_functions(*args):
-    """ an arbitrary function """
-    print("Hi, this is an arbitrary function.")
-    for _ in args:
-        print(_)
+def a_demo_function(*args):
+    """ a demo function """
+    return None
diff --git a/csst_proto/top_level_interface.py b/csst_proto/top_level_interface.py
index 471997ff71bfc6edb04305e408cbbbe690c2640d..6180569aa97f66874c8f6d002c54c66511aedca9 100644
--- a/csst_proto/top_level_interface.py
+++ b/csst_proto/top_level_interface.py
@@ -1,5 +1,5 @@
 from .flip_image import flip_image, read_test_image
-from .some_other_modules import an_arbitrary_functions
+from .some_other_modules import a_demo_function
 
 
-__all__ = ["flip_image", "read_test_image", "an_arbitrary_functions"]
+__all__ = ["flip_image", "read_test_image", "a_demo_function"]
diff --git a/tests/test_other_functions.py b/tests/test_other_functions.py
new file mode 100644
index 0000000000000000000000000000000000000000..6b773893ac8571420c0db0c9f3cb0fc584dbe712
--- /dev/null
+++ b/tests/test_other_functions.py
@@ -0,0 +1,11 @@
+import unittest
+
+from csst_proto.top_level_interface import a_demo_function
+
+
+class TestCaseDemoFunction(unittest.TestCase):
+    def test_demo_function(self):
+        # flip test image
+        self.assertTrue(
+            a_demo_function(1) is None
+        )