422,
                    detail={
                        "name": "ContentSizeLimitExceeded",
                        "code": 999,
                        "message": "File limit exceeded",
                    },
                )
            return message

        return inner

    async def __call__(self, scope, receive, send):

```Python hl_lines="3"
{!../../../docs_src/app_testing/test_main.py!}
```

...and have the code for the tests just like before.

## Testing: extended example

Now let's extend this example and add more details to see how to test different parts.

### Extended **FastAPI** app file

Let's continue with the same file structure as before:

```
.
├── app
│   ├── __init__.py
│   ├── main.py

class ExtendedItem(Item):
    age: int


@app.post("/items/")
def save_union_different_body(item: Union[ExtendedItem, Item]):
    return {"item": item}


client = TestClient(app)


def test_post_extended_item():
    response = client.post("/items/", json={"name": "Foo", "age": 5})
    assert response.status_code == 200, response.text
    assert response.json() == {"item": {"name": "Foo", "age": 5}}

def on_page_markdown(
    markdown: str, *, page: Page, config: MkDocsConfig, files: Files
) -> str:
    if isinstance(page.file, EnFile):
        for excluded_section in non_traslated_sections:
            if page.file.src_path.startswith(excluded_section):
                return markdown
        missing_translation_content = get_missing_translation_content(config.docs_dir)
        header = ""
        body = markdown