More informative assert errors for WebsocketCommunicator.

channels/testing/websocket.py

@@ -78,27 +78,33 @@ async def receive_from(self, timeout=1):
         """
         response = await self.receive_output(timeout)
         # Make sure this is a send message
-        assert response["type"] == "websocket.send"
+        assert (
+            response["type"] == "websocket.send"
+        ), f"Expected type 'websocket.send', but was '{response['type']}'"
         # Make sure there's exactly one key in the response
         assert ("text" in response) != (
             "bytes" in response
         ), "The response needs exactly one of 'text' or 'bytes'"
         # Pull out the right key and typecheck it for our users
         if "text" in response:
-            assert isinstance(response["text"], str), "Text frame payload is not str"
+            assert isinstance(
+                response["text"], str
+            ), f"Text frame payload is not str, it is {type(response['text'])}"
             return response["text"]
         else:
             assert isinstance(
                 response["bytes"], bytes
-            ), "Binary frame payload is not bytes"
+            ), f"Binary frame payload is not bytes, it is {type(response['bytes'])}"
             return response["bytes"]
 
     async def receive_json_from(self, timeout=1):
         """
         Receives a JSON text frame payload and decodes it
         """
         payload = await self.receive_from(timeout)
-        assert isinstance(payload, str), "JSON data is not a text frame"
+        assert isinstance(
+            payload, str
+        ), f"JSON data is not a text frame, it is {type(payload)}"
         return json.loads(payload)
 
     async def disconnect(self, code=1000, timeout=1):

tests/test_testing.py

@@ -47,6 +47,13 @@ def receive(self, text_data=None, bytes_data=None):
         self.send(text_data=text_data, bytes_data=bytes_data)
 
 
+class AcceptCloseWebsocketApp(WebsocketConsumer):
+    def connect(self):
+        assert self.scope["path"] == "/testws/"
+        self.accept()
+        self.close()
+
+
 class ErrorWebsocketApp(WebsocketConsumer):
     """
     Barebones WebSocket ASGI app for error testing.
@@ -93,6 +100,24 @@ async def test_websocket_communicator():
     await communicator.disconnect()
 
 
+@pytest.mark.django_db
+@pytest.mark.asyncio
+async def test_websocket_incorrect_read_json():
+    """
+    Tests that when using invalid communicator method, assertion error is gonna be raised with informative message.
+    In this test, server accepts and then immediately closes the connection so the server is not in valid state
+    to handle "receive_from".
+    """
+    communicator = WebsocketCommunicator(AcceptCloseWebsocketApp(), "/testws/")
+    await communicator.connect()
+    with pytest.raises(AssertionError) as exception_info:
+        await communicator.receive_from()
+    assert (
+        str(exception_info.value)
+        == "Expected type 'websocket.send', but was 'websocket.close'"
+    )
+
+
 @pytest.mark.django_db
 @pytest.mark.asyncio
 async def test_websocket_application():