test: add test for duplicate operation ID fix with multi-method routes

tests/test_duplicate_operation_id.py

@@ -0,0 +1,56 @@
+"""Test for fix of issue #13175: duplicate operation IDs with multi-method routes"""
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+
+def test_no_duplicate_operation_ids_with_multiple_methods():
+    """Test that routes with multiple methods generate unique operation IDs for each method."""
+    app = FastAPI()
+
+    @app.api_route("/items/", methods=["GET", "POST", "DELETE"])
+    def handle_items():
+        return {"message": "handled"}
+
+    client = TestClient(app)
+    response = client.get("/openapi.json")
+    assert response.status_code == 200
+    
+    data = response.json()
+    
+    # Check that all three methods exist in the OpenAPI schema
+    paths = data.get("paths", {})
+    items_path = paths.get("/items/", {})
+    
+    assert "get" in items_path
+    assert "post" in items_path
+    assert "delete" in items_path
+    
+    # Verify each method has a unique operation ID
+    get_op_id = items_path["get"].get("operationId")
+    post_op_id = items_path["post"].get("operationId")
+    delete_op_id = items_path["delete"].get("operationId")
+    
+    # All should exist
+    assert get_op_id is not None
+    assert post_op_id is not None
+    assert delete_op_id is not None
+    
+    # All should be different
+    assert get_op_id != post_op_id
+    assert get_op_id != delete_op_id
+    assert post_op_id != delete_op_id
+    
+    # Verify they follow the pattern: <name>_<path>_<method>
+    assert "handle_items_items_" in get_op_id
+    assert "handle_items_items_" in post_op_id
+    assert "handle_items_items_" in delete_op_id
+    
+    assert "_get" in get_op_id
+    assert "_post" in post_op_id
+    assert "_delete" in delete_op_id
+
+
+if __name__ == "__main__":
+    test_no_duplicate_operation_ids_with_multiple_methods()
+    print("✓ Test passed!")
+