An example could be that you have an external authentication provider that you need to call.

You send it a token and it returns an authenticated user.

This provider might be charging you per request, and calling it might take some extra time than if you had a fixed mock user for tests.

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

    this.closeables = closeables;
  }

  /**
   * Returns a future that finishes when this step does. Calling {@code get()} on the returned
   * future returns {@code null} if the step is successful or throws the same exception that would
   * be thrown by calling {@code finishToFuture().get()} if this were the last step. Calling {@code
   * cancel()} on the returned future has no effect on the {@code ClosingFuture} pipeline.
   *

     * LF<? extends @Nullable V>. That might be better: There's currently no difference between the
     * outputs users get when calling this with <Foo> and calling it with <@Nullable Foo>. The only
     * difference is that calling it with <Foo> won't work when an input Future has a @Nullable
     * type. So why even make that error possible by giving callers the choice?
     *

     * LF<? extends @Nullable V>. That might be better: There's currently no difference between the
     * outputs users get when calling this with <Foo> and calling it with <@Nullable Foo>. The only
     * difference is that calling it with <Foo> won't work when an input Future has a @Nullable
     * type. So why even make that error possible by giving callers the choice?
     *

  /**
   * Any interruption that happens as a result of calling interruptTask will arrive before this
   * method is called. Complete Futures here.
   */
  abstract void afterRanInterruptiblySuccess(@ParametricNullness T result);

  /**
   * Any interruption that happens as a result of calling interruptTask will arrive before this
   * method is called. Complete Futures here.
   */

		}
	}

	log.Debug("calling CreateInpodRules")
	if err := s.netnsRunner(openNetns, func() error {
		return s.podIptables.CreateInpodRules(log, HostProbeSNATIP, HostProbeSNATIPV6, ingressMode)
	}); err != nil {
		log.Errorf("failed to update POD inpod: %s/%s %v", pod.Namespace, pod.Name, err)
		return err
	}

	// For *any* failures after calling `CreateInpodRules`, we must return PartialAdd error.

  /**
   * Any interruption that happens as a result of calling interruptTask will arrive before this
   * method is called. Complete Futures here.
   */
  abstract void afterRanInterruptiblySuccess(@ParametricNullness T result);

  /**
   * Any interruption that happens as a result of calling interruptTask will arrive before this
   * method is called. Complete Futures here.
   */

But **FastAPI** will know that it has to solve `query_extractor` first, to pass the results of that to `query_or_cookie_extractor` while calling it.

///

```mermaid
graph TB

query_extractor(["query_extractor"])
query_or_cookie_extractor(["query_or_cookie_extractor"])

read_query["/items/"]

/**
 * Collects problems that are encountered during model building. The primary purpose of this component is to account for
 * the fact that the problem reporter has/should not have information about the calling context and hence cannot provide
 * an expressive source hint for the model problem. Instead, the source hint is configured by the model builder before

/// tip

You'll see what other "things", apart from functions, can be used as dependencies in the next chapter.

///

Whenever a new request arrives, **FastAPI** will take care of:

* Calling your dependency ("dependable") function with the correct parameters.
* Get the result from your function.
* Assign that result to the parameter in your *path operation function*.

```mermaid
graph TB