The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

## Other Asynchronous Function Calls

As the testing function is now asynchronous, you can now also call (and `await`) other `async` functions apart from sending requests to your FastAPI application in your tests, exactly as you would call them anywhere else in your code.

!!! tip

### Other utility functions

Any other utility function that you call directly can be created with normal `def` or `async def` and FastAPI won't affect the way you call it.

This is in contrast to the functions that FastAPI calls for you: *path operation functions* and dependencies.

You probably want to test the external provider once, but not necessarily call it for every test that runs.

In this case, you can override the dependency that calls that provider, and use a custom dependency that returns a mock user, only for your tests.

### Use the `app.dependency_overrides` attribute

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="19"
    {!> ../../../docs_src/dependencies/tutorial002.py!}
    ```

**FastAPI** calls the `CommonQueryParams` class. This creates an "instance" of that class and the instance will be passed as the parameter `commons` to your function.

## Type annotation vs `Depends`

          path: ./site/**

  # https://github.com/marketplace/actions/alls-green#why
  docs-all-green:  # This job does nothing and is only used for the branch protection
    if: always()
    needs:
      - build-docs
    runs-on: ubuntu-latest
    steps:
      - name: Decide whether the needed jobs succeeded or failed
        uses: re-actors/alls-green@release/v1
        with:
          jobs: ${{ toJSON(needs) }}

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="1  10"
    {!> ../../../docs_src/settings/app03/main.py!}
    ```

Then for any subsequent calls of `get_settings()` in the dependencies for the next requests, instead of executing the internal code of `get_settings()` and creating a new `Settings` object, it will return the same object that was returned on the first call, again and again.

            by_alias: bool = True,
            exclude_unset: bool = False,
            exclude_defaults: bool = False,
            exclude_none: bool = False,
        ) -> Any:
            # What calls this code passes a value that already called
            # self._type_adapter.validate_python(value)
            return self._type_adapter.dump_python(
                value,
                mode=mode,