Testing

Testing Channels consumers is a little trickier than testing normal Django views due to their underlying asynchronous nature.

To help with testing, Channels provides test helpers called Communicators, which allow you to wrap up an ASGI application (like a consumer) into its own event loop and ask it questions.

They do, however, require that you have asynchronous support in your test suite. While you can do this yourself, we recommend using py.test with its asyncio plugin, which is how we’ll illustrate tests below.

Setting Up Async Tests

Firstly, you need to get py.test set up with async test support, and presumably Django test support as well. You can do this by installing the pytest-django and pytest-asyncio packages:

pip install -U pytest-django pytest-asyncio

Then, you need to decorate the tests you want to run async with pytest.mark.asyncio. Note that you can’t mix this with unittest.TestCase subclasses; you have to write async tests as top-level test functions in the native py.test style:

import pytest
from channels.testing import HttpCommunicator
from myproject.myapp.consumers import MyConsumer

@pytest.mark.asyncio
async def test_my_consumer():
    communicator = HttpCommunicator(MyConsumer, "GET", "/test/")
    response = await communicator.get_response()
    assert response["body"] == b"test response"
    assert response["status"] == 200

If you have normal Django views, you can continue to test those with the standard Django test tools and client. You only need the async setup for code that’s written as consumers.

There’s a few variants of the Communicator - a plain one for generic usage, and one each for HTTP and WebSockets specifically that have shortcut methods,

ApplicationCommunicator

ApplicationCommunicator is the generic test helper for any ASGI application. It provides several basic methods for interaction as explained below.

You should only need this generic class for non-HTTP/WebSocket tests, though you might need to fall back to it if you are testing things like HTTP chunked responses or long-polling, which aren’t supported in HttpCommunicator yet.

Note

ApplicationCommunicator is actually provided by the base asgiref package, but we let you import it from channels.testing for convenience.

To construct it, pass it an application and a scope:

from channels.testing import ApplicationCommunicator
communicator = ApplicationCommunicator(MyConsumer, {"type": "http", ...})

send_input

Call it to send an event to the application:

await communicator.send_input({
    "type": "http.request",
    "body": b"chunk one \x01 chunk two",
})

receive_output

Call it to receive an event from the application:

event = await communicator.receive_output(timeout=1)
assert event["type"] == "http.response.start"

receive_nothing

Call it to check that there is no event waiting to be received from the application:

assert await communicator.receive_nothing(timeout=0.1, interval=0.01) is False
# Receive the rest of the http request from above
event = await communicator.receive_output()
assert event["type"] == "http.response.body"
assert event.get("more_body") is True
event = await communicator.receive_output()
assert event["type"] == "http.response.body"
assert event.get("more_body") is None
# Check that there isn't another event
assert await communicator.receive_nothing() is True
# You could continue to send and receive events
# await communicator.send_input(...)

The method has two optional parameters:

  • timeout: number of seconds to wait to ensure the queue is empty. Defaults to 0.1.
  • interval: number of seconds to wait for another check for new events. Defaults to 0.01.

wait

Call it to wait for an application to exit (you’ll need to either do this or wait for it to send you output before you can see what it did using mocks or inspection):

await communicator.wait(timeout=1)

If you’re expecting your application to raise an exception, use pytest.raises around wait:

with pytest.raises(ValueError):
    await communicator.wait()

HttpCommunicator

HttpCommunicator is a subclass of ApplicationCommunicator specifically tailored for HTTP requests. You need only instantiate it with your desired options:

from channels.testing import HttpCommunicator
communicator = HttpCommunicator(MyHttpConsumer, "GET", "/test/")

And then wait for its response:

response = await communicator.get_response()
assert response["body"] == b"test response"

You can pass the following arguments to the constructor:

  • method: HTTP method name (unicode string, required)
  • path: HTTP path (unicode string, required)
  • body: HTTP body (bytestring, optional)

The response from the get_response method will be a dict with the following keys:

* ``status``: HTTP status code (integer)
* ``headers``: List of headers as (name, value) tuples (both bytestrings)
* ``body``: HTTP response body (bytestring)

WebsocketCommunicator

WebsocketCommunicator allows you to more easily test WebSocket consumers. It provides several convenience methods for interacting with a WebSocket application, as shown in this example:

from channels.testing import WebsocketCommunicator
communicator = WebsocketCommunicator(SimpleWebsocketApp, "/testws/")
connected, subprotocol = await communicator.connect()
assert connected
# Test sending text
await communicator.send_to(text_data="hello")
response = await communicator.receive_from()
assert response == "hello"
# Close
await communicator.disconnect()

Note

All of these methods are coroutines, which means you must await them. If you do not, your test will either time out (if you forgot to await a send) or try comparing things to a coroutine object (if you forgot to await a receive).

Important

If you don’t call WebsocketCommunicator.disconnect() before your test suite ends, you may find yourself getting RuntimeWarnings about things never being awaited, as you will be killing your app off in the middle of its lifecycle. You do not, however, have to disconnect() if your app already raised an error.

You can also pass an application built with URLRouter instead of the plain consumer class. This lets you test applications that require positional or keyword arguments in the scope:

from channels.testing import WebsocketCommunicator
application = URLRouter([
    url(r"^testws/(?P<message>\w+)/$", KwargsWebSocketApp),
])
communicator = WebsocketCommunicator(application, "/testws/test/")
assert connected
# Test on connection welcome message
message = await communicator.receive_from()
assert message == 'test'
# Close
await communicator.disconnect()

Note

Since the WebsocketCommunicator class takes a URL in its contructor, a single Communicator can only test a single URL. If you want to test multiple different URLs, use multiple Communicators.

connect

Triggers the connection phase of the WebSocket and waits for the application to either accept or deny the connection. Takes no parameters and returns either:

  • (True, <chosen_subprotocol>) if the socket was accepted. chosen_subprotocol defaults to None.
  • (False, <close_code>) if the socket was rejected. close_code defaults to 1000.

send_to

Sends a data frame to the application. Takes exactly one of bytes_data or text_data as parameters, and returns nothing:

await communicator.send_to(bytes_data=b"hi\0")

This method will type-check your parameters for you to ensure what you are sending really is text or bytes.

send_json_to

Sends a JSON payload to the application as a text frame. Call it with an object and it will JSON-encode it for you, and return nothing:

await communicator.send_json_to({"hello": "world"})

receive_from

Receives a frame from the application and gives you either bytes or text back depending on the frame type:

response = await communicator.receive_from()

Takes an optional timeout argument with a number of seconds to wait before timing out, which defaults to 1. It will typecheck your application’s responses for you as well, to ensure that text frames contain text data, and binary frames contain binary data.

receive_json_from

Receives a text frame from the application and decodes it for you:

response = await communicator.receive_json_from()
assert response == {"hello": "world"}

Takes an optional timeout argument with a number of seconds to wait before timing out, which defaults to 1.

receive_nothing

Checks that there is no frame waiting to be received from the application. For details see ApplicationCommunicator.

disconnect

Closes the socket from the client side. Takes nothing and returns nothing.

You do not need to call this if the application instance you’re testing already exited (for example, if it errored), but if you do call it, it will just silently return control to you.

ChannelsLiveServerTestCase

If you just want to run standard Selenium or other tests that require a webserver to be running for external programs, you can use ChannelsLiveServerTestCase, which is a drop-in replacement for the standard Django LiveServerTestCase:

from channels.testing import ChannelsLiveServerTestCase

class SomeLiveTests(ChannelsLiveServerTestCase):

    def test_live_stuff(self):
        call_external_testing_thing(self.live_server_url)

Note

You can’t use an in-memory database for your live tests. Therefore include a test database file name in your settings to tell Django to use a file database if you use SQLite:

DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.sqlite3",
        "NAME": os.path.join(BASE_DIR, "db.sqlite3"),
        "TEST": {
            "NAME": os.path.join(BASE_DIR, "db_test.sqlite3"),
        },
    },
}

serve_static

Subclass ChannelsLiveServerTestCase with serve_static = True in order to serve static files (comparable to Django’s StaticLiveServerTestCase, you don’t need to run collectstatic before or as a part of your tests setup).