fix(test): add router.acancel_batch coverage (#20183)

- Add test_router_acancel_batch.py with mock test for router.acancel_batch()
- Add _acancel_batch to ignored list (internal helper tested via public API)

Fixes CI failure in check_code_and_doc_quality job

tests/code_coverage_tests/router_code_coverage.py

@@ -74,6 +74,7 @@ def get_functions_from_router(file_path):
 
 
 ignored_function_names = [
+    "_acancel_batch",
     "__init__",
 ]
 

tests/router_unit_tests/test_router_acancel_batch.py

@@ -0,0 +1,53 @@
+"""
+Test router.acancel_batch() functionality
+
+This ensures the router's batch cancellation method has test coverage.
+"""
+import sys
+import os
+
+sys.path.insert(0, os.path.abspath("../.."))
+
+import pytest
+from unittest.mock import patch, AsyncMock, MagicMock
+from litellm import Router
+import litellm
+
+
+@pytest.fixture
+def router():
+    """Create a router with a mock deployment"""
+    return Router(
+        model_list=[
+            {
+                "model_name": "gpt-4",
+                "litellm_params": {
+                    "model": "gpt-4",
+                    "api_key": "fake-key",
+                },
+            }
+        ]
+    )
+
+
+@pytest.mark.asyncio
+async def test_router_acancel_batch(router):
+    """Test that router.acancel_batch() calls litellm.acancel_batch with correct params"""
+    mock_response = MagicMock()
+    mock_response.id = "batch_123"
+    mock_response.status = "cancelled"
+    
+    with patch.object(litellm, "acancel_batch", new_callable=AsyncMock) as mock_cancel:
+        mock_cancel.return_value = mock_response
+        
+        # This tests that the router method exists and can be called
+        # The actual API call is mocked
+        response = await router.acancel_batch(
+            model="gpt-4",
+            batch_id="batch_123",
+        )
+        
+        # Verify the mock was called
+        assert mock_cancel.called
+        assert response.id == "batch_123"
+        assert response.status == "cancelled"