Added test coverage to additional_response issue

tests/test_additional_responses_no_mutation.py

@@ -0,0 +1,165 @@
+"""
+Regression test: Ensure app-level responses with Union models and content/examples
+don't accumulate duplicate $ref entries in anyOf arrays.
+See https://github.com/fastapi/fastapi/pull/14463
+"""
+
+from fastapi import FastAPI
+from pydantic import BaseModel
+
+from fastapi.testclient import TestClient
+
+
+class ModelA(BaseModel):
+    a: str
+
+
+class ModelB(BaseModel):
+    b: str
+
+
+app = FastAPI(
+    responses={
+        500: {
+            'model': ModelA | ModelB,
+            'content': {"application/json": {
+                'examples': {"Case A": {"value": "a"}}
+            }}
+        }
+    }
+)
+
+
+@app.get('/route1')
+def route1():
+    return "test"
+
+
+@app.get('/route2')
+def route2():
+    return "test"
+
+
+client = TestClient(app)
+
+
+def test_openapi_schema():
+    response = client.get("/openapi.json")
+    assert response.status_code == 200, response.text
+    assert response.json() == {
+        "openapi": "3.1.0",
+        "info": {
+            "title": "FastAPI",
+            "version": "0.1.0"
+        },
+        "paths": {
+            "/route1": {
+                "get": {
+                    "summary": "Route1",
+                    "operationId": "route1_route1_get",
+                    "responses": {
+                        "200": {
+                            "description": "Successful Response",
+                            "content": {
+                                "application/json": {
+                                    "schema": {}
+                                }
+                            }
+                        },
+                        "500": {
+                            "description": "Internal Server Error",
+                            "content": {
+                                "application/json": {
+                                    "schema": {
+                                        "anyOf": [
+                                            {
+                                                "$ref": "#/components/schemas/ModelA"
+                                            },
+                                            {
+                                                "$ref": "#/components/schemas/ModelB"
+                                            }
+                                        ],
+                                        "title": "Response 500 Route1 Route1 Get"
+                                    },
+                                    "examples": {
+                                        "Case A": {
+                                            "value": "a"
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            },
+            "/route2": {
+                "get": {
+                    "summary": "Route2",
+                    "operationId": "route2_route2_get",
+                    "responses": {
+                        "200": {
+                            "description": "Successful Response",
+                            "content": {
+                                "application/json": {
+                                    "schema": {}
+                                }
+                            }
+                        },
+                        "500": {
+                            "description": "Internal Server Error",
+                            "content": {
+                                "application/json": {
+                                    "schema": {
+                                        "anyOf": [
+                                            {
+                                                "$ref": "#/components/schemas/ModelA"
+                                            },
+                                            {
+                                                "$ref": "#/components/schemas/ModelB"
+                                            }
+                                        ],
+                                        "title": "Response 500 Route2 Route2 Get"
+                                    },
+                                    "examples": {
+                                        "Case A": {
+                                            "value": "a"
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        },
+        "components": {
+            "schemas": {
+                "ModelA": {
+                    "properties": {
+                        "a": {
+                            "type": "string",
+                            "title": "A"
+                        }
+                    },
+                    "type": "object",
+                    "required": [
+                        "a"
+                    ],
+                    "title": "ModelA"
+                },
+                "ModelB": {
+                    "properties": {
+                        "b": {
+                            "type": "string",
+                            "title": "B"
+                        }
+                    },
+                    "type": "object",
+                    "required": [
+                        "b"
+                    ],
+                    "title": "ModelB"
+                }
+            }
+        }
+    }