Create functions with a name that starts with `test_` (this is standard `pytest` conventions).

Use the `TestClient` object the same way as you do with `httpx`.

Write simple `assert` statements with the standard Python expressions that you need to check (again, standard `pytest`).

{* ../../docs_src/app_testing/tutorial001_py39.py hl[2,12,15:18] *}

/// tip

Notice that the testing functions are normal `def`, not `async def`.

 * using the latest values obtained from {@link IteratorTester#newTargetIterator()}.
 *
 * <p>The value you pass to the parameter {@code steps} should be greater than the length of your
 * iterator, so that this class can check that your iterator behaves correctly when it is exhausted.
 *
 * <p>For example, to test {@link java.util.Collections#unmodifiableList(java.util.List)
 * Collections.unmodifiableList}'s iterator:
 *

///

It will:

* Return that status code in the response.
* Document it as such in the OpenAPI schema (and so, in the user interfaces):

<img src="/img/tutorial/response-status-code/image01.png">

/// note

Some response codes (see the next section) indicate that the response does not have a body.

FastAPI knows this, and will produce OpenAPI docs that state there is no response body.

///

      } else {
        return false;
      }
    }

    private boolean equalsTypeVariable(TypeVariable<?> that) {
      return var.getGenericDeclaration().equals(that.getGenericDeclaration())
          && var.getName().equals(that.getName());
    }
  }

## Mounting a **FastAPI** application { #mounting-a-fastapi-application }

"Mounting" means adding a completely "independent" application in a specific path, that then takes care of handling everything under that path, with the _path operations_ declared in that sub-application.

### Top-level application { #top-level-application }

First, create the main, top-level, **FastAPI** application, and its *path operations*:

Note that the go_darwin_$GOARCH_exec wrapper uninstalls any existing app identified by
the bundle id before installing a new app. If the uninstalled app is the last app by
the developer identity, the device might also remove the permission to run apps from
that developer, and the exec wrapper will fail to install the new app. To avoid that,

   *
   * <p>The returned iterable's iterator supports {@code remove()} if the iterator of the underlying
   * iterable supports it. Note that it is <i>not</i> possible to delete the last skipped element by
   * immediately calling {@code remove()} on that iterator, as the {@code Iterator} contract states

  - type: textarea
    attributes:
      label: 1. What are you trying to do?
    validations:
      required: true

  - type: textarea
    attributes:
      label: 2. What's the best code you can write to accomplish that without the new feature?
    validations:
      required: true

  - type: textarea
    attributes:
      label: 3. What would that same code look like if we added your feature?
    validations:

   * Internet users can register subdomains. An example of a public suffix that is not a registry
   * suffix is {@code blogspot.com}. Note that it is true that all public suffixes <i>have</i>
   * registry suffixes, since domain name registries collectively control all internet domain names.
   *

You can also create an environment variable only for a **specific program invocation**, that is only available to that program, and only for its duration.

To do that, create it right before the program itself, on the same line:

<div class="termy">

```console
// Create an env var MY_NAME in line for this program call