peer.acceptFrame() // ACK
    peer.sendFrame().ping(false, 2, 3)
    peer.acceptFrame() // PING
    peer.play()

    // Play it back.
    connect(peer)

    // Verify the peer received what was expected.
    val ping = peer.takeFrame()
    assertThat(ping.type).isEqualTo(Http2.TYPE_PING)
    assertThat(ping.streamId).isEqualTo(0)
    assertThat(ping.payload1).isEqualTo(2)

  - type: textarea
    id: current-behavior
    attributes:
      label: Current Behavior
      description: Tell us what happens
    validations:
      required: true
  - type: textarea
    id: expected-behavior
    attributes:
      label: Expected Behavior
      description: Tell us what should happen
    validations:
      required: true
  - type: textarea
    id: context
    attributes:

 maven.repo.local      (system,user,default=${maven.user.config.dir}/repository)

 We need to define what happens in the when things are not setup correctly

 o ~/.m2 directory does not exist
 o ~/.m2/maven.properties does not exist
 o if they once existed but now to do not exist

    ```

The last `CommonQueryParams`, in:

```Python
... Depends(CommonQueryParams)
```

...is what **FastAPI** will actually use to know what is the dependency.

From it is that FastAPI will extract the declared parameters and that is what FastAPI will actually call.

---

In this case, the first `CommonQueryParams`, in:

=== "Python 3.8+"

    ```Python

  - type: textarea
    id: current-behavior
    attributes:
      label: Current Behavior
      description: Tell us what happens
    validations:
      required: true
  - type: textarea
    id: expected-behavior
    attributes:
      label: Expected Behavior
      description: Tell us what should happen
    validations:
      required: true
  - type: textarea
    id: context
    attributes:

// errLessData - returned when less data available than what was requested.
var errLessData = StorageErr("less data available than what was requested")

// errMoreData = returned when more data was sent by the caller than what it was supposed to.
var errMoreData = StorageErr("more data was sent than what was advertised")

// indicates readDirFn to return without further applying the fn()

 * #iterator()} method after the first, and whose iterator is always unmodifiable.
 *
 * <p>The {@code Iterable} specification does not make it absolutely clear what should happen on a
 * second invocation, so implementors have made various choices, including:
 *
 * <ul>
 *   <li>returning the same iterator again
 *   <li>throwing an exception of some kind

But most importantly:

* It will **limit and filter** the output data to what is defined in the return type.
    * This is particularly important for **security**, we'll see more of that below.

## `response_model` Parameter

There are some cases where you need or want to return some data that is not exactly what the type declares.

In this case, you could want to document how that external API *should* look like. What *path operation* it should have, what body it should expect, what response it should return, etc.

## An app with callbacks

Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

    suite.addTestSuite(MutableClassToInstanceMapTest.class);

    suite.addTest(
        MapTestSuiteBuilder.using(
                new TestClassToInstanceMapGenerator() {
                  // Other tests will verify what real, warning-free usage looks like
                  // but here we have to do some serious fudging
                  @Override
                  @SuppressWarnings({"unchecked", "rawtypes"})