How to use the priority.DuplicateStreamError function in priority

def test_priority_tree_raises_error_inserting_duplicate(self):
        """
        Attempting to insert a stream that is already in the tree raises a
        DuplicateStreamError
        """
        p = priority.PriorityTree()
        p.insert_stream(1)

        with pytest.raises(priority.DuplicateStreamError):
            p.insert_stream(1)

def insert_stream(self, stream_id):
        try:
            self.tree.insert_stream(stream_id)
        except priority.DuplicateStreamError:
            assert stream_id in self.stream_ids
        else:
            assert stream_id not in self.stream_ids
            self.stream_ids.add(stream_id)

"""
        stream = H2Stream(
            event.stream_id,
            self, event.headers,
            self.requestFactory,
            self.site,
            self.factory
        )
        self.streams[event.stream_id] = stream
        self._streamCleanupCallbacks[event.stream_id] = Deferred()
        self._outboundStreamQueues[event.stream_id] = deque()

        # Add the stream to the priority tree but immediately block it.
        try:
            self.priority.insert_stream(event.stream_id)
        except priority.DuplicateStreamError:
            # Stream already in the tree. This can happen if we received a
            # PRIORITY frame before a HEADERS frame. Just move on: we set the
            # stream up properly in _handlePriorityUpdate.
            pass
        else:
            self.priority.block(event.stream_id)

"""
        stream = H2Stream(
            event.stream_id,
            self, event.headers,
            self.requestFactory,
            self.site,
            self.factory
        )
        self.streams[event.stream_id] = stream
        self._streamCleanupCallbacks[event.stream_id] = Deferred()
        self._outboundStreamQueues[event.stream_id] = deque()

        # Add the stream to the priority tree but immediately block it.
        try:
            self.priority.insert_stream(event.stream_id)
        except priority.DuplicateStreamError:
            # Stream already in the tree. This can happen if we received a
            # PRIORITY frame before a HEADERS frame. Just move on: we set the
            # stream up properly in _handlePriorityUpdate.
            pass
        else:
            self.priority.block(event.stream_id)

received request.
        @type event: L{h2.events.RequestReceived}
        """
        stream = H2Stream(
            event.stream_id, self, event.headers, self.requestFactory
        )
        stream.site = self.site
        stream.factory = self.factory
        self.streams[event.stream_id] = stream
        self._streamCleanupCallbacks[event.stream_id] = Deferred()
        self._outboundStreamQueues[event.stream_id] = deque()

        # Add the stream to the priority tree but immediately block it.
        try:
            self.priority.insert_stream(event.stream_id)
        except priority.DuplicateStreamError:
            # Stream already in the tree. This can happen if we received a
            # PRIORITY frame before a HEADERS frame. Just move on: we set the
            # stream up properly in _handlePriorityUpdate.
            pass
        else:
            self.priority.block(event.stream_id)

request.stream_id,
            )
        else:
            self.streams[request.stream_id] = HTTPStream(
                self.config,
                self.ssl,
                self.client,
                self.server,
                self.stream_send,
                self.spawn_app,
                request.stream_id,
            )
        self.stream_buffers[request.stream_id] = StreamBuffer(self.event_class)
        try:
            self.priority.insert_stream(request.stream_id)
        except priority.DuplicateStreamError:
            # Recieved PRIORITY frame before HEADERS frame
            pass
        else:
            self.priority.block(request.stream_id)

        await self.streams[request.stream_id].handle(
            Request(
                stream_id=request.stream_id,
                headers=filter_pseudo_headers(request.headers),
                http_version="2",
                method=method,
                raw_path=raw_path,
            )