PlainSerializer(lambda v: v.data),
    ]

    class MyModel(BaseModel):
        model_config = ConfigDict(arbitrary_types_allowed=True)
        custom_field: FakeNumpyArrayPydantic

    app = FastAPI()

    @app.get("/")
    def test() -> MyModel:
        return MyModel(custom_field=FakeNumpyArray())

    client = TestClient(app)
    return client