diff --git a/tests/router_unit_tests/test_router_endpoints.py b/tests/router_unit_tests/test_router_endpoints.py
index de1d22d5a8..0b60d5b26f 100644
--- a/tests/router_unit_tests/test_router_endpoints.py
+++ b/tests/router_unit_tests/test_router_endpoints.py
@@ -665,3 +665,53 @@ async def test_init_vector_store_api_endpoints():
         custom_llm_provider="openai"
     )
 
+
+def test_apply_default_settings():
+    """
+    Test the apply_default_settings method.
+    
+    This test verifies that apply_default_settings correctly initializes
+    default pre-call checks and doesn't modify existing router state.
+    """
+    # Test with fresh router
+    router = Router()
+    initial_optional_callbacks = router.optional_callbacks
+    
+    # Test that the method runs without error
+    result = router.apply_default_settings()
+    
+    # Verify method returns None as expected
+    assert result is None
+    
+    # Verify that optional_callbacks remains None if it was initially None
+    # (since default_pre_call_checks is an empty list)
+    assert router.optional_callbacks == initial_optional_callbacks
+    
+    # Test with router that already has some optional_callbacks
+    router_with_callbacks = Router()
+    mock_callback = MagicMock()
+    router_with_callbacks.optional_callbacks = [mock_callback]
+    
+    # Apply default settings
+    result = router_with_callbacks.apply_default_settings()
+    
+    # Verify method returns None
+    assert result is None
+    
+    # Verify existing callbacks are preserved (since we're adding empty list)
+    assert mock_callback in router_with_callbacks.optional_callbacks
+    
+    # Test that the method is called during router initialization
+    with patch.object(Router, 'apply_default_settings') as mock_apply:
+        Router()
+        mock_apply.assert_called_once()
+    
+    # Test with mocked add_optional_pre_call_checks to verify internal call
+    router_test = Router()
+    with patch.object(router_test, 'add_optional_pre_call_checks') as mock_add_checks:
+        router_test.apply_default_settings()
+        
+        # Verify add_optional_pre_call_checks was called with empty list
+        mock_add_checks.assert_called_once_with([])
+
+