if handler == nil {
		return nil, ErrUnknownHandler
	}

	var requests chan []byte
	var responses chan Response
	if handler.InCapacity > 0 {
		requests = make(chan []byte, handler.InCapacity)
	}
	if handler.OutCapacity > 0 {
		responses = make(chan Response, handler.OutCapacity)
	} else {
		responses = make(chan Response, 1)
	}

	cl, err := c.newMuxClient(ctx)
	if err != nil {
		return nil, err
	}

    client = TestClient(app)
    return client


@needs_pydanticv2
def test_filter_sub_model(client: TestClient):
    response = client.get("/model/modelA")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "name": "modelA",
        "description": "model-a-desc",
        "foo": {"username": "test-user"},
    }


@needs_pydanticv2

        .build(),
    )
    val call1 =
      client.newCall(
        Request.Builder()
          .url(server.url("/"))
          .build(),
      )
    val response1 = call1.execute()
    assertThat(response1.body.string()).isEqualTo("abc")
    response1.close()

    // Force a fresh connection for the next request.
    client.connectionPool.evictAll()

  fun finishRequest()

  /**
   * Parses bytes of a response header from an HTTP transport.
   *
   * @param expectContinue true to return null if this is an intermediate response with a "100"
   * response code. Otherwise this method never returns null.
   */
  @Throws(IOException::class)
  fun readResponseHeaders(expectContinue: Boolean): Response.Builder?

  @Throws(IOException::class)

        }
    )


def test_openapi_schema():
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {
            "/items/": {
                "post": {
                    "responses": {
                        "200": {

    Note over client,operation: Response is already sent, can't change it anymore
    opt Tasks
        operation -->> tasks: Send background tasks
    end
    opt Raise other exception
        tasks -->> tasks: Handle exceptions in the background task code
    end
```

/// info

Only **one response** will be sent to the client. It might be one of the error responses or it will be the response from the *path operation*.

	}
	// Start processing requests.
	close(processHandler)

	// Drain responses
	got := 0
	for resp := range st.responses {
		// t.Log("got response", resp)
		errFatal(resp.Err)
		if resp.Msg[0] != byte(got) {
			t.Error("expected response", got, "got", resp.Msg[0])
		}
		got++
	}
	if got != 100 {
		t.Error("expected 100 responses, got", got)
	}
}

def test_openapi_schema(client: TestClient):
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {
            "/files/": {
                "post": {
                    "responses": {
                        "200": {

@needs_py39
def test_openapi_schema(client: TestClient):
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {
            "/files/": {
                "post": {
                    "responses": {
                        "200": {

```

////

Notice that the *path operations* define the models they use for request payload and response payload, using the models `Item` and `ResponseMessage`.

### API Docs

If you go to the API docs, you will see that it has the **schemas** for the data to be sent in requests and received in responses:

<img src="/img/tutorial/generate-clients/image01.png">