val response1 = client.newCall(request1).execute()
    assertThat(response1.code).isEqualTo(401)
    assertThat(response1.body.string())
      .isEqualTo("{\"error\":{\"message\":\"No auth credentials found\",\"code\":401}}")

    val request2 = request1.newBuilder().header("Authorization", "XYZ").build()
    val response2 = client.newCall(request2).execute()

        assertEquals(0, response.writeDataWireFormat(null, 0));

        // Read methods return 0 without accessing null buffer
        assertEquals(0, response.readSetupWireFormat(null, 0, 0));
        assertEquals(0, response.readParametersWireFormat(null, 0, 0));
        assertEquals(0, response.readDataWireFormat(null, 0, 0));
    }

    @Test

# `Response` class

You can declare a parameter in a *path operation function* or dependency to be of type `Response` and then you can set data for the response like headers or cookies.

You can also use it directly to create an instance of it and return it from your *path operations*.

You can import it directly from `fastapi`:

```python
from fastapi import Response
```

    server.enqueue(MockResponse(body = "response that will never be received"))
    val response = executeSynchronously("/")
    response.assertFailure(
      // JDK 11 response to the FAIL_HANDSHAKE:
      SSLException::class.java,
      // RI response to the FAIL_HANDSHAKE:
      SSLProtocolException::class.java,
      // Android's response to the FAIL_HANDSHAKE:
      SSLHandshakeException::class.java,

            // When & Then
            assertEquals(0, response.writeBytesWireFormat(dst, 0));
            assertEquals(0, response.writeBytesWireFormat(dst, 25));
            assertEquals(0, response.writeBytesWireFormat(dst, 50));
            assertEquals(0, response.writeBytesWireFormat(dst, 75));
            assertEquals(0, response.writeBytesWireFormat(dst, 99));
        }

        @Test

        for additional_status_code, response in self.responses.items():
            assert isinstance(response, dict), "An additional response must be a dict"
            model = response.get("model")
            if model:
                assert is_body_allowed_for_status_code(additional_status_code), (
                    f"Status code {additional_status_code} must not have a response body"
                )

async def dep0(response: Response):
    response.headers["x-level0"] = "True"


async def dep1(response: Response):
    response.headers["x-level1"] = "True"


async def dep2(response: Response):
    response.headers["x-level2"] = "True"


async def dep3(response: Response):
    response.headers["x-level3"] = "True"


async def dep4(response: Response):

    assert "redoc@2" in response.text


def test_enum_status_code_response():
    response = client.get("/enum-status-code")
    assert response.status_code == 201, response.text
    assert response.json() == "foo bar"


def test_openapi_schema():
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text

def test_a():
    response = client.get("/a")
    assert response.status_code == 200, response.text
    assert response.json() == "a"


def test_b():
    response = client.get("/b")
    assert response.status_code == 200, response.text
    assert response.json() == "b"


def test_c():
    response = client.get("/c")
    assert response.status_code == 200, response.text
    assert response.json() == "c"

# Custom Response - HTML, Stream, File, others { #custom-response-html-stream-file-others }

By default, **FastAPI** will return the responses using `JSONResponse`.

You can override it by returning a `Response` directly as seen in [Return a Response directly](response-directly.md){.internal-link target=_blank}.