diff --git a/tests/basic/test_coder.py b/tests/basic/test_coder.py
index 0e540035f..4befc2342 100644
--- a/tests/basic/test_coder.py
+++ b/tests/basic/test_coder.py
@@ -189,6 +189,30 @@ class TestCoder(unittest.TestCase):
 
             self.assertEqual(coder.abs_fnames, set([str(fname.resolve())]))
 
+    def test_check_for_file_mentions_read_only(self):
+        with GitTemporaryDirectory():
+            io = InputOutput(pretty=False, yes=False)  # Set yes=False to simulate user not confirming
+            coder = Coder.create(self.GPT35, None, io)
+
+            fname = Path("readonly_file.txt")
+            fname.touch()
+
+            coder.abs_read_only_fnames.add(str(fname.resolve()))
+
+            # Mock the get_tracked_files method
+            mock = MagicMock()
+            mock.return_value = set([str(fname)])
+            coder.repo.get_tracked_files = mock
+
+            # Call the check_for_file_mentions method
+            result = coder.check_for_file_mentions(f"Please check {fname}!")
+
+            # Assert that the method returns None (user not asked to add the file)
+            self.assertIsNone(result)
+
+            # Assert that abs_fnames is still empty (file not added)
+            self.assertEqual(coder.abs_fnames, set())
+
     def test_check_for_subdir_mention(self):
         with GitTemporaryDirectory():
             io = InputOutput(pretty=False, yes=True)