assert not override4 or "x-level4" in response.headers
    assert not override5 or "x-level5" in response.headers


def test_openapi():
    client = TestClient(app)
    with warnings.catch_warnings(record=True) as w:
        warnings.simplefilter("always")
        response = client.get("/openapi.json")
        assert issubclass(w[-1].category, UserWarning)
        assert "Duplicate Operation ID" in str(w[-1].message)

lot more going on, processing the request and response, handling dependencies, executing **your own code**, and particularly, **waiting for the network**. But you will probably still get some nice performance improvements just from the upgrade.

The focus of this release is **compatibility** with Pydantic v1 and v2, to make sure your current apps keep working. Later there will be more focus on refactors, correctness, code improvements, and then **performance** improvements. Some third-party...