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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 

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 
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def __init__(
    self,
    app: ASGIApp,
    base_url: str = "http://testserver",
    raise_server_exceptions: bool = True,
    root_path: str = "",
    backend: typing.Literal["asyncio", "trio"] = "asyncio",
    backend_options: dict[str, typing.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 = typing.cast(ASGI2App, app)  # type: ignore[assignment]
        asgi_app = _WrapASGI2(app)  # type: ignore[arg-type]
    self.app = asgi_app
    self.app_state: dict[str, typing.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 

headers

HTTP headers to include when sending requests.

follow_redirects instance-attribute 

follow_redirects = follow_redirects

max_redirects instance-attribute 

max_redirects = max_redirects

is_closed property 

is_closed

Check if the client being closed

trust_env property 

trust_env

timeout property writable 

timeout

event_hooks property writable 

event_hooks

auth property writable 

auth

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

See also Authentication.

base_url property writable 

base_url

Base URL to use when sending requests with relative URLs.

cookies property writable 

cookies

Cookie values to include when sending requests.

params property writable 

params

Query parameters to include in the URL when sending requests.

task instance-attribute 

task

portal class-attribute instance-attribute 

portal = None

async_backend instance-attribute 

async_backend = _AsyncBackend(
    backend=backend, backend_options=backend_options or {}
)

app instance-attribute 

app = asgi_app

app_state instance-attribute 

app_state = {}

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 
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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 

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 
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@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 

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 
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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 

close()

Close transport and proxies.

Source code in httpx/_client.py 
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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 

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
)
Source code in starlette/testclient.py 
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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: typing.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, typing.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/encode/starlette/issues/1108 for more information.",
            DeprecationWarning,
        )
    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 

get(
    url,
    *,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
Source code in starlette/testclient.py 
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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, typing.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 

options(
    url,
    *,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
Source code in starlette/testclient.py 
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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, typing.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 

head(
    url,
    *,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
Source code in starlette/testclient.py 
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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, typing.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 

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
)
Source code in starlette/testclient.py 
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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: typing.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, typing.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 

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
)
Source code in starlette/testclient.py 
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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: typing.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, typing.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 

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
)
Source code in starlette/testclient.py 
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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: typing.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, typing.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 

delete(
    url,
    *,
    params=None,
    headers=None,
    cookies=None,
    auth=USE_CLIENT_DEFAULT,
    follow_redirects=USE_CLIENT_DEFAULT,
    timeout=USE_CLIENT_DEFAULT,
    extensions=None
)
Source code in starlette/testclient.py 
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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, typing.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 

websocket_connect(url, subprotocols=None, **kwargs)
Source code in starlette/testclient.py 
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def websocket_connect(
    self,
    url: str,
    subprotocols: typing.Sequence[str] | None = None,
    **kwargs: typing.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 

lifespan()
Source code in starlette/testclient.py 
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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 

wait_startup()
Source code in starlette/testclient.py 
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async def wait_startup(self) -> None:
    await self.stream_receive.send({"type": "lifespan.startup"})

    async def receive() -> typing.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 

wait_shutdown()
Source code in starlette/testclient.py 
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async def wait_shutdown(self) -> None:
    async def receive() -> typing.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()