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Test Client - TestClient¶

You can use the TestClient class to test FastAPI applications without creating an actual HTTP and socket connection, just communicating directly with the FastAPI code.

Read more about it in the FastAPI docs for Testing.

You can import it directly from fastapi.testclient:

from fastapi.testclient import TestClient

fastapi.testclient.TestClient

Section titled “fastapi.testclient.TestClient ¶”
TestClient(
    app,
    base_url="http://testserver",
    raise_server_exceptions=True,
    root_path="",
    backend="asyncio",
    backend_options=None,
    cookies=None,
    headers=None,
    follow_redirects=True,
    client=("testclient", 50000),
)

Bases: Client

Source code in starlette/testclient.py
def __init__(
    self,
    app: ASGIApp,
    base_url: str = "http://testserver",
    raise_server_exceptions: bool = True,
    root_path: str = "",
    backend: Literal["asyncio", "trio"] = "asyncio",
    backend_options: dict[str, Any] | None = None,
    cookies: httpx._types.CookieTypes | None = None,
    headers: dict[str, str] | None = None,
    follow_redirects: bool = True,
    client: tuple[str, int] = ("testclient", 50000),
) -> None:
    self.async_backend = _AsyncBackend(backend=backend, backend_options=backend_options or {})
    if _is_asgi3(app):
        asgi_app = app
    else:
        app = cast(ASGI2App, app)  # type: ignore[assignment]
        asgi_app = _WrapASGI2(app)  # type: ignore[arg-type]
    self.app = asgi_app
    self.app_state: dict[str, Any] = {}
    transport = _TestClientTransport(
        self.app,
        portal_factory=self._portal_factory,
        raise_server_exceptions=raise_server_exceptions,
        root_path=root_path,
        app_state=self.app_state,
        client=client,
    )
    if headers is None:
        headers = {}
    headers.setdefault("user-agent", "testclient")
    super().__init__(
        base_url=base_url,
        headers=headers,
        transport=transport,
        follow_redirects=follow_redirects,
        cookies=cookies,
    )

headers property writable

Section titled “headers property writable ¶”
headers

HTTP headers to include when sending requests.

follow_redirects instance-attribute

Section titled “follow_redirects instance-attribute ¶”
follow_redirects = follow_redirects

max_redirects instance-attribute

Section titled “max_redirects instance-attribute ¶”
max_redirects = max_redirects

is_closed property

Section titled “is_closed property ¶”
is_closed

Check if the client being closed

trust_env property

Section titled “trust_env property ¶”
trust_env

timeout property writable

Section titled “timeout property writable ¶”
timeout

event_hooks property writable

Section titled “event_hooks property writable ¶”
event_hooks

auth property writable

Section titled “auth property writable ¶”
auth

Authentication class used when none is passed at the request-level.

See also Authentication.

base_url property writable

Section titled “base_url property writable ¶”
base_url

Base URL to use when sending requests with relative URLs.

cookies property writable

Section titled “cookies property writable ¶”
cookies

Cookie values to include when sending requests.

params property writable

Section titled “params property writable ¶”
params

Query parameters to include in the URL when sending requests.

task instance-attribute

Section titled “task instance-attribute ¶”
task

portal class-attribute instance-attribute

Section titled “portal class-attribute instance-attribute ¶”
portal = None

async_backend instance-attribute

Section titled “async_backend instance-attribute ¶”
async_backend = _AsyncBackend(
    backend=backend, backend_options=backend_options or {}
)

app instance-attribute

Section titled “app instance-attribute ¶”
app = asgi_app

app_state instance-attribute

Section titled “app_state instance-attribute ¶”
app_state = {}

build_request

Section titled “build_request ¶”
build_request(
    method,
    url,
    *,
    content=None,
    data=None,
    files=None,
    json=None,
    params=None,
    headers=None,
    cookies=None,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)

Build and return a request instance.

  • The params, headers and cookies arguments are merged with any values set on the client.
  • The url argument is merged with any base_url set on the client.

See also: Request instances

Source code in httpx/_client.py
def build_request(
    self,
    method: str,
    url: URL | str,
    *,
    content: RequestContent | None = None,
    data: RequestData | None = None,
    files: RequestFiles | None = None,
    json: typing.Any | None = None,
    params: QueryParamTypes | None = None,
    headers: HeaderTypes | None = None,
    cookies: CookieTypes | None = None,
    timeout: TimeoutTypes | UseClientDefault = USE_CLIENT_DEFAULT,
    extensions: RequestExtensions | None = None,
) -> Request:
    """
    Build and return a request instance.

    * The `params`, `headers` and `cookies` arguments
    are merged with any values set on the client.
    * The `url` argument is merged with any `base_url` set on the client.

    See also: [Request instances][0]

    [0]: /advanced/clients/#request-instances
    """
    url = self._merge_url(url)
    headers = self._merge_headers(headers)
    cookies = self._merge_cookies(cookies)
    params = self._merge_queryparams(params)
    extensions = {} if extensions is None else extensions
    if "timeout" not in extensions:
        timeout = (
            self.timeout
            if isinstance(timeout, UseClientDefault)
            else Timeout(timeout)
        )
        extensions = dict(**extensions, timeout=timeout.as_dict())
    return Request(
        method,
        url,
        content=content,
        data=data,
        files=files,
        json=json,
        params=params,
        headers=headers,
        cookies=cookies,
        extensions=extensions,
    )

stream

Section titled “stream ¶”
stream(
    method,
    url,
    *,
    content=None,
    data=None,
    files=None,
    json=None,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)

Alternative to httpx.request() that streams the response body instead of loading it into memory at once.

Parameters: See httpx.request.

See also: Streaming Responses

Source code in httpx/_client.py
@contextmanager
def stream(
    self,
    method: str,
    url: URL | str,
    *,
    content: RequestContent | None = None,
    data: RequestData | None = None,
    files: RequestFiles | None = None,
    json: typing.Any | None = None,
    params: QueryParamTypes | None = None,
    headers: HeaderTypes | None = None,
    cookies: CookieTypes | None = None,
    auth: AuthTypes | UseClientDefault | None = USE_CLIENT_DEFAULT,
    follow_redirects: bool | UseClientDefault = USE_CLIENT_DEFAULT,
    timeout: TimeoutTypes | UseClientDefault = USE_CLIENT_DEFAULT,
    extensions: RequestExtensions | None = None,
) -> typing.Iterator[Response]:
    """
    Alternative to `httpx.request()` that streams the response body
    instead of loading it into memory at once.

    **Parameters**: See `httpx.request`.

    See also: [Streaming Responses][0]

    [0]: /quickstart#streaming-responses
    """
    request = self.build_request(
        method=method,
        url=url,
        content=content,
        data=data,
        files=files,
        json=json,
        params=params,
        headers=headers,
        cookies=cookies,
        timeout=timeout,
        extensions=extensions,
    )
    response = self.send(
        request=request,
        auth=auth,
        follow_redirects=follow_redirects,
        stream=True,
    )
    try:
        yield response
    finally:
        response.close()

send

Section titled “send ¶”
send(
    request,
    *,
    stream=False,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT
)

Send a request.

The request is sent as-is, unmodified.

Typically you'll want to build one with Client.build_request() so that any client-level configuration is merged into the request, but passing an explicit httpx.Request() is supported as well.

See also: Request instances

Source code in httpx/_client.py
def send(
    self,
    request: Request,
    *,
    stream: bool = False,
    auth: AuthTypes | UseClientDefault | None = USE_CLIENT_DEFAULT,
    follow_redirects: bool | UseClientDefault = USE_CLIENT_DEFAULT,
) -> Response:
    """
    Send a request.

    The request is sent as-is, unmodified.

    Typically you'll want to build one with `Client.build_request()`
    so that any client-level configuration is merged into the request,
    but passing an explicit `httpx.Request()` is supported as well.

    See also: [Request instances][0]

    [0]: /advanced/clients/#request-instances
    """
    if self._state == ClientState.CLOSED:
        raise RuntimeError("Cannot send a request, as the client has been closed.")

    self._state = ClientState.OPENED
    follow_redirects = (
        self.follow_redirects
        if isinstance(follow_redirects, UseClientDefault)
        else follow_redirects
    )

    self._set_timeout(request)

    auth = self._build_request_auth(request, auth)

    response = self._send_handling_auth(
        request,
        auth=auth,
        follow_redirects=follow_redirects,
        history=[],
    )
    try:
        if not stream:
            response.read()

        return response

    except BaseException as exc:
        response.close()
        raise exc

close

Section titled “close ¶”
close()

Close transport and proxies.

Source code in httpx/_client.py
def close(self) -> None:
    """
    Close transport and proxies.
    """
    if self._state != ClientState.CLOSED:
        self._state = ClientState.CLOSED

        self._transport.close()
        for transport in self._mounts.values():
            if transport is not None:
                transport.close()

request

Section titled “request ¶”
request(
    method,
    url,
    *,
    content=None,
    data=None,
    files=None,
    json=None,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
code
def request(  # type: ignore[override]
    self,
    method: str,
    url: httpx._types.URLTypes,
    *,
    content: httpx._types.RequestContent | None = None,
    data: _RequestData | None = None,
    files: httpx._types.RequestFiles | None = None,
    json: Any = None,
    params: httpx._types.QueryParamTypes | None = None,
    headers: httpx._types.HeaderTypes | None = None,
    cookies: httpx._types.CookieTypes | None = None,
    auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    extensions: dict[str, Any] | None = None,
) -> httpx.Response:
    if timeout is not httpx.USE_CLIENT_DEFAULT:
        warnings.warn(
            "You should not use the 'timeout' argument with the TestClient. "
            "See https://github.com/Kludex/starlette/issues/1108 for more information.",
            StarletteDeprecationWarning,
            stacklevel=2,
        )
    url = self._merge_url(url)
    return super().request(
        method,
        url,
        content=content,
        data=data,
        files=files,
        json=json,
        params=params,
        headers=headers,
        cookies=cookies,
        auth=auth,
        follow_redirects=follow_redirects,
        timeout=timeout,
        extensions=extensions,
    )

get

Section titled “get ¶”
get(
    url,
    *,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
code
def get(  # type: ignore[override]
    self,
    url: httpx._types.URLTypes,
    *,
    params: httpx._types.QueryParamTypes | None = None,
    headers: httpx._types.HeaderTypes | None = None,
    cookies: httpx._types.CookieTypes | None = None,
    auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    extensions: dict[str, Any] | None = None,
) -> httpx.Response:
    return super().get(
        url,
        params=params,
        headers=headers,
        cookies=cookies,
        auth=auth,
        follow_redirects=follow_redirects,
        timeout=timeout,
        extensions=extensions,
    )

options

Section titled “options ¶”
options(
    url,
    *,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
code
def options(  # type: ignore[override]
    self,
    url: httpx._types.URLTypes,
    *,
    params: httpx._types.QueryParamTypes | None = None,
    headers: httpx._types.HeaderTypes | None = None,
    cookies: httpx._types.CookieTypes | None = None,
    auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    extensions: dict[str, Any] | None = None,
) -> httpx.Response:
    return super().options(
        url,
        params=params,
        headers=headers,
        cookies=cookies,
        auth=auth,
        follow_redirects=follow_redirects,
        timeout=timeout,
        extensions=extensions,
    )

head

Section titled “head ¶”
head(
    url,
    *,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
code
def head(  # type: ignore[override]
    self,
    url: httpx._types.URLTypes,
    *,
    params: httpx._types.QueryParamTypes | None = None,
    headers: httpx._types.HeaderTypes | None = None,
    cookies: httpx._types.CookieTypes | None = None,
    auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    extensions: dict[str, Any] | None = None,
) -> httpx.Response:
    return super().head(
        url,
        params=params,
        headers=headers,
        cookies=cookies,
        auth=auth,
        follow_redirects=follow_redirects,
        timeout=timeout,
        extensions=extensions,
    )

post

Section titled “post ¶”
post(
    url,
    *,
    content=None,
    data=None,
    files=None,
    json=None,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
code
def post(  # type: ignore[override]
    self,
    url: httpx._types.URLTypes,
    *,
    content: httpx._types.RequestContent | None = None,
    data: _RequestData | None = None,
    files: httpx._types.RequestFiles | None = None,
    json: Any = None,
    params: httpx._types.QueryParamTypes | None = None,
    headers: httpx._types.HeaderTypes | None = None,
    cookies: httpx._types.CookieTypes | None = None,
    auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    extensions: dict[str, Any] | None = None,
) -> httpx.Response:
    return super().post(
        url,
        content=content,
        data=data,
        files=files,
        json=json,
        params=params,
        headers=headers,
        cookies=cookies,
        auth=auth,
        follow_redirects=follow_redirects,
        timeout=timeout,
        extensions=extensions,
    )

put

Section titled “put ¶”
put(
    url,
    *,
    content=None,
    data=None,
    files=None,
    json=None,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
code
def put(  # type: ignore[override]
    self,
    url: httpx._types.URLTypes,
    *,
    content: httpx._types.RequestContent | None = None,
    data: _RequestData | None = None,
    files: httpx._types.RequestFiles | None = None,
    json: Any = None,
    params: httpx._types.QueryParamTypes | None = None,
    headers: httpx._types.HeaderTypes | None = None,
    cookies: httpx._types.CookieTypes | None = None,
    auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    extensions: dict[str, Any] | None = None,
) -> httpx.Response:
    return super().put(
        url,
        content=content,
        data=data,
        files=files,
        json=json,
        params=params,
        headers=headers,
        cookies=cookies,
        auth=auth,
        follow_redirects=follow_redirects,
        timeout=timeout,
        extensions=extensions,
    )

patch

Section titled “patch ¶”
patch(
    url,
    *,
    content=None,
    data=None,
    files=None,
    json=None,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
code
def patch(  # type: ignore[override]
    self,
    url: httpx._types.URLTypes,
    *,
    content: httpx._types.RequestContent | None = None,
    data: _RequestData | None = None,
    files: httpx._types.RequestFiles | None = None,
    json: Any = None,
    params: httpx._types.QueryParamTypes | None = None,
    headers: httpx._types.HeaderTypes | None = None,
    cookies: httpx._types.CookieTypes | None = None,
    auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    extensions: dict[str, Any] | None = None,
) -> httpx.Response:
    return super().patch(
        url,
        content=content,
        data=data,
        files=files,
        json=json,
        params=params,
        headers=headers,
        cookies=cookies,
        auth=auth,
        follow_redirects=follow_redirects,
        timeout=timeout,
        extensions=extensions,
    )

delete

Section titled “delete ¶”
delete(
    url,
    *,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
code
def delete(  # type: ignore[override]
    self,
    url: httpx._types.URLTypes,
    *,
    params: httpx._types.QueryParamTypes | None = None,
    headers: httpx._types.HeaderTypes | None = None,
    cookies: httpx._types.CookieTypes | None = None,
    auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
    extensions: dict[str, Any] | None = None,
) -> httpx.Response:
    return super().delete(
        url,
        params=params,
        headers=headers,
        cookies=cookies,
        auth=auth,
        follow_redirects=follow_redirects,
        timeout=timeout,
        extensions=extensions,
    )

websocket_connect

Section titled “websocket_connect ¶”
websocket_connect(url, subprotocols=None, **kwargs)
code
def websocket_connect(
    self,
    url: str,
    subprotocols: Sequence[str] | None = None,
    **kwargs: Any,
) -> WebSocketTestSession:
    url = urljoin("ws://testserver", url)
    headers = kwargs.get("headers", {})
    headers.setdefault("connection", "upgrade")
    headers.setdefault("sec-websocket-key", "testserver==")
    headers.setdefault("sec-websocket-version", "13")
    if subprotocols is not None:
        headers.setdefault("sec-websocket-protocol", ", ".join(subprotocols))
    kwargs["headers"] = headers
    try:
        super().request("GET", url, **kwargs)
    except _Upgrade as exc:
        session = exc.session
    else:
        raise RuntimeError("Expected WebSocket upgrade")  # pragma: no cover

    return session

lifespan async

Section titled “lifespan async ¶”
lifespan()
code
async def lifespan(self) -> None:
    scope = {"type": "lifespan", "state": self.app_state}
    try:
        await self.app(scope, self.stream_receive.receive, self.stream_send.send)
    finally:
        await self.stream_send.send(None)

wait_startup async

Section titled “wait_startup async ¶”
wait_startup()
code
async def wait_startup(self) -> None:
    await self.stream_receive.send({"type": "lifespan.startup"})

    async def receive() -> Any:
        message = await self.stream_send.receive()
        if message is None:
            self.task.result()
        return message

    message = await receive()
    assert message["type"] in (
        "lifespan.startup.complete",
        "lifespan.startup.failed",
    )
    if message["type"] == "lifespan.startup.failed":
        await receive()

wait_shutdown async

Section titled “wait_shutdown async ¶”
wait_shutdown()
code
async def wait_shutdown(self) -> None:
    async def receive() -> Any:
        message = await self.stream_send.receive()
        if message is None:
            self.task.result()
        return message

    await self.stream_receive.send({"type": "lifespan.shutdown"})
    message = await receive()
    assert message["type"] in (
        "lifespan.shutdown.complete",
        "lifespan.shutdown.failed",
    )
    if message["type"] == "lifespan.shutdown.failed":
        await receive()
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