```txt
Hello, World from Flask!
```

And if you go to <a href="http://localhost:8000/v2" class="external-link" target="_blank">http://localhost:8000/v2</a> you will see the response from FastAPI:

```JSON
{
    "message": "Hello World"
}

@app.get("/app")
def read_main(request: Request):
    return {"message": "Hello World", "root_path": request.scope.get("root_path")}


client = TestClient(app)


def test_main():
    response = client.get("/app")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello World", "root_path": "/api/v1"}


def test_openapi():
    response = client.get("/openapi.json")

```txt
Hello, World from Flask!
```

并且如果您访问 <a href="http://localhost:8000/v2" class="external-link" target="_blank">http://localhost:8000/v2</a>，您将会看到由 FastAPI 返回的响应：

```JSON
{
    "message": "Hello World"
}

     * @param request The model building request that holds the parameters, must not be {@code null}.
     * @return The result of the model building, never {@code null}.
     * @throws ModelBuildingException If the effective model could not be built.
     */
    ModelBuildingResult build(ModelBuildingRequest request) throws ModelBuildingException;

    /**

     * @param scope the {link PathScope} to collect dependencies, must not be {@code null}
     * @return the collection result, never {@code null}
     * @throws DependencyResolverException if the dependency tree could not be built
     * @throws IllegalArgumentException if an argument is null or invalid
     * @see #collect(DependencyResolverRequest)
     */
    @Nonnull
    default DependencyResolverResult collect(

## Deployment Strategies { #deployment-strategies }

There are several ways to do it depending on your specific use case and the tools that you use.

You could **deploy a server** yourself using a combination of tools, you could use a **cloud service** that does part of the work for you, or other possible options.

    assert response.json() == {"message": "Hello World"}
    assert (
        response.headers["access-control-allow-origin"]
        == "https://localhost.tiangolo.com"
    )

    # Test non-CORS response
    response = client.get("/")
    assert response.status_code == 200, response.text
    assert response.json() == {"message": "Hello World"}

     * @param options The options to use for serialization, may be {@code null} to use the default values.
     * @param model The model to serialize, must not be {@code null}.
     * @throws IOException If the model could not be serialized.
     */
    void write(File output, Map<String, Object> options, Model model) throws IOException;

    /**

     * @return The populated execution request, never {@code null}.
     * @throws MavenExecutionRequestPopulationException If the execution request could not be populated.
     * @since 3.3.0
     */
    MavenExecutionRequest populateFromToolchains(MavenExecutionRequest request, PersistedToolchains toolchains)
            throws MavenExecutionRequestPopulationException;

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def root():