The test client allows you to make requests against your ASGI application, using the `requests` library. ```python from starlette.responses import HTMLResponse from starlette.testclient import TestClient class App: def __init__(self, scope): self.scope = scope async def __call__(self, receive, send): response = HTMLResponse('Hello, world!') await response(receive, send) def test_app(): client = TestClient(App) response = client.get('/') assert response.status_code == 200 ``` The test client exposes the same interface as any other `requests` session. In particular, note that the calls to make a request are just standard function calls, not awaitables. You can use any of `requests` standard API, such as authentication, session cookies handling, or file uploads. By default the `TestClient` will raise any exceptions that occur in the application. Occasionally you might want to test the content of 500 error responses, rather than allowing client to raise the server exception. In this case you should use `client = TestClient(app, raise_server_exceptions=False)`. ### Testing WebSocket sessions You can also test websocket sessions with the test client. The `requests` library will be used to build the initial handshake, meaning you can use the same authentication options and other headers between both http and websocket testing. ```python from starlette.testclient import TestClient from starlette.websockets import WebSocket class App: def __init__(self, scope): self.scope = scope async def __call__(self, receive, send): websocket = WebSocket(self.scope, receive=receive, send=send) await websocket.accept() await websocket.send_text('Hello, world!') await websocket.close() def test_app(): client = TestClient(App) with client.websocket_connect('/') as websocket: data = websocket.receive_text() assert data == 'Hello, world!' ``` The operations on session are standard function calls, not awaitables. It's important to use the session within a context-managed `with` block. This ensure that the background thread on which the ASGI application is properly terminated, and that any exceptions that occur within the application are always raised by the test client. #### Establishing a test session * `.websocket_connect(url, subprotocols=None, **options)` - Takes the same set of arguments as `requests.get()`. May raise `starlette.websockets.Disconnect` if the application does not accept the websocket connection. #### Sending data * `.send_text(data)` - Send the given text to the application. * `.send_bytes(data)` - Send the given bytes to the application. * `.send_json(data)` - Send the given data to the application. #### Receiving data * `.receive_text()` - Wait for incoming text sent by the application and return it. * `.receive_bytes()` - Wait for incoming bytestring sent by the application and return it. * `.receive_json()` - Wait for incoming json data sent by the application and return it. May raise `starlette.websockets.Disconnect`. #### Closing the connection * `.close(code=1000)` - Perform a client-side close of the websocket connection.