partial fixes

Author: pavel-kirienko

CLAUDE.md

@@ -22,7 +22,8 @@ Concrete transports are in top-level submodules:
 - `pycyphal.udp` — Cyphal/UDP transport implementation.
 - `pycyphal.can` (coming soon, not yet in the codebase) — Cyphal/CAN transport implementation.
 
-The core must be dependency-free. Transports may introduce (optional) dependencies.
+The core must be dependency-free.
+Transports may introduce (optional) dependencies that MUST be kept to the bare minimum.
 
 Internal implementation modules use leading underscores.
 Keep public symbols explicit through `__init__.py`; keep private helpers in underscore-prefixed modules.
@@ -37,6 +38,11 @@ between modules, even if they are not intended for external use.
 DO NOT access protected members externally. If you need access, make the required members public.
 Remember this does not contaminate the API in this design.
 
+All I/O is async/await (pytest-asyncio with `asyncio_mode="auto"`).
+The code is fully type-annotated; frozen dataclasses for data.
+
+Formatting follows PEP8, enforced using Black, line-length=120.
+
 ## Reference design
 
 `reference/` contains git submodules with the reference implementations in C of the session layer (`cy/`)
@@ -49,20 +55,17 @@ Expected usage patterns:
 - Review-only audit: Use `$cyphal-parity-guard` to review parity vs reference and report discrepancies.
 - Sync/fix pass: Use `$cyphal-parity-guard` to bring implementation in sync with the reference and add regression tests for every divergence fixed.
 
-## Conventions
-
-Formatting follows PEP8, enforced using Black, line-length=120.
-
-All I/O is async/await (pytest-asyncio with `asyncio_mode="auto"`).
-The code is fully type-annotated; frozen dataclasses for data.
-Dependencies intentionally kept to the bare minimum.
-
 ### Testing
 
 Mock transport/network in `tests/conftest.py`.
 Tests are x10+ the size of source code and must provide full coverage of the core.
 Transport test coverage is more opportunistic.
 
+The library must ONLY be tested with Python versions starting from the minimum specified in `pyproject.toml`
+up to the current latest stable Python. TESTING ON UNSUPPORTED VERSIONS IS NOT ALLOWED.
+
+Work will not be accepted unless `nox` (without arguments) runs successfully.
+
 ### Logging
 
 Logging is required throughout the codebase; prefer many short messages. Avoid adding logging statements on code

tests/conftest.py

@@ -1,200 +1,26 @@
-"""Mock transport and network for testing."""
+"""Pytest fixtures for the test suite."""
 
 from __future__ import annotations
 
 import asyncio
-import random
-from collections.abc import Callable
 
 import pytest
 
-from pycyphal import Closable, Instant, Priority, TransportArrival
-
-# A small prime modulus suitable for testing.
-DEFAULT_MODULUS = 122743
-
-
-# =====================================================================================================================
-# MockSubjectWriter
-# =====================================================================================================================
-
-
-class MockSubjectWriter(Closable):
-    def __init__(self, transport: MockTransport, subject_id: int) -> None:
-        self.transport = transport
-        self.subject_id = subject_id
-        self.closed = False
-        self.send_count = 0
-        self.fail_next = False
-
-    async def __call__(self, deadline: Instant, priority: Priority, message: bytes | memoryview) -> None:
-        if self.closed:
-            raise RuntimeError("Writer closed")
-        if self.fail_next:
-            self.fail_next = False
-            raise RuntimeError("Simulated send failure")
-        self.send_count += 1
-        msg_bytes = bytes(message)
-        arrival = TransportArrival(
-            timestamp=Instant.now(),
-            priority=priority,
-            remote_id=self.transport.node_id,
-            message=msg_bytes,
-        )
-        # Deliver to all listeners on this subject across the network
-        if self.transport.network is not None:
-            self.transport.network.deliver_subject(self.subject_id, arrival, sender=self.transport)
-        else:
-            # Local-only delivery
-            for handler in self.transport._subject_handlers.get(self.subject_id, []):
-                handler(arrival)
-
-    def close(self) -> None:
-        self.closed = True
-
-
-# =====================================================================================================================
-# MockSubjectListener
-# =====================================================================================================================
-
-
-class MockSubjectListener(Closable):
-    def __init__(self, transport: MockTransport, subject_id: int, handler: Callable[[TransportArrival], None]) -> None:
-        self.transport = transport
-        self.subject_id = subject_id
-        self.handler = handler
-        self.closed = False
-
-    def close(self) -> None:
-        self.closed = True
-        handlers = self.transport._subject_handlers.get(self.subject_id, [])
-        if self.handler in handlers:
-            handlers.remove(self.handler)
-        if not handlers:
-            self.transport._subject_handlers.pop(self.subject_id, None)
-
-
-# =====================================================================================================================
-# MockTransport
-# =====================================================================================================================
-
-
-class MockTransport(Closable):
-    def __init__(self, node_id: int = 0, modulus: int = DEFAULT_MODULUS, network: MockNetwork | None = None) -> None:
-        self.node_id = node_id
-        self._modulus = modulus
-        self.network = network
-        self._subject_handlers: dict[int, list[Callable[[TransportArrival], None]]] = {}
-        self._unicast_handler: Callable[[TransportArrival], None] | None = None
-        self._writers: dict[int, MockSubjectWriter] = {}
-        self.unicast_log: list[tuple[int, bytes]] = []
-        self.closed = False
-        self.fail_unicast = False
-
-        if network is not None:
-            network.add_transport(self)
-
-    @property
-    def subject_id_modulus(self) -> int:
-        return self._modulus
-
-    def subject_listen(self, subject_id: int, handler: Callable[[TransportArrival], None]) -> Closable:
-        if subject_id not in self._subject_handlers:
-            self._subject_handlers[subject_id] = []
-        self._subject_handlers[subject_id].append(handler)
-        return MockSubjectListener(self, subject_id, handler)
-
-    def subject_advertise(self, subject_id: int) -> MockSubjectWriter:
-        writer = MockSubjectWriter(self, subject_id)
-        self._writers[subject_id] = writer
-        return writer
-
-    def unicast_listen(self, handler: Callable[[TransportArrival], None]) -> None:
-        self._unicast_handler = handler
-
-    async def unicast(self, deadline: Instant, priority: Priority, remote_id: int, message: bytes | memoryview) -> None:
-        if self.closed:
-            raise RuntimeError("Transport closed")
-        if self.fail_unicast:
-            raise RuntimeError("Simulated unicast failure")
-        msg_bytes = bytes(message)
-        self.unicast_log.append((remote_id, msg_bytes))
-        arrival = TransportArrival(
-            timestamp=Instant.now(),
-            priority=priority,
-            remote_id=self.node_id,
-            message=msg_bytes,
-        )
-        if self.network is not None:
-            self.network.deliver_unicast(remote_id, arrival)
-        else:
-            # Local unicast: deliver to own handler
-            if self._unicast_handler is not None:
-                self._unicast_handler(arrival)
-
-    def close(self) -> None:
-        self.closed = True
-
-    def deliver_subject(self, subject_id: int, arrival: TransportArrival) -> None:
-        """Deliver a subject message to local handlers."""
-        for handler in self._subject_handlers.get(subject_id, []):
-            handler(arrival)
-
-    def deliver_unicast(self, arrival: TransportArrival) -> None:
-        """Deliver a unicast message to local handler."""
-        if self._unicast_handler is not None:
-            self._unicast_handler(arrival)
-
-
-# =====================================================================================================================
-# MockNetwork
-# =====================================================================================================================
-
-
-class MockNetwork:
-    """Simulates a network connecting multiple MockTransport instances."""
-
-    def __init__(self, *, delay: float = 0.0, drop_rate: float = 0.0) -> None:
-        self.transports: dict[int, MockTransport] = {}
-        self.delay = delay
-        self.drop_rate = drop_rate
-        self.message_log: list[tuple[str, int, bytes]] = []
-
-    def add_transport(self, transport: MockTransport) -> None:
-        self.transports[transport.node_id] = transport
-
-    def deliver_subject(self, subject_id: int, arrival: TransportArrival, sender: MockTransport) -> None:
-        """Deliver subject message to all transports (including sender for loopback)."""
-        for tid, transport in self.transports.items():
-            if random.random() < self.drop_rate:
-                continue
-            transport.deliver_subject(subject_id, arrival)
-
-    def deliver_unicast(self, remote_id: int, arrival: TransportArrival) -> None:
-        """Deliver unicast message to specific transport."""
-        transport = self.transports.get(remote_id)
-        if transport is not None:
-            if random.random() >= self.drop_rate:
-                transport.deliver_unicast(arrival)
-
-
-# =====================================================================================================================
-# Fixtures
-# =====================================================================================================================
+from tests.mock_transport import MockTransport, MockNetwork
 
 
 @pytest.fixture
-def mock_network():
+def mock_network() -> MockNetwork:
     return MockNetwork()
 
 
 @pytest.fixture
-def mock_transport():
+def mock_transport() -> MockTransport:
     return MockTransport(node_id=1)
 
 
 @pytest.fixture
-def event_loop():
+def event_loop():  # type: ignore[no-untyped-def]
     loop = asyncio.new_event_loop()
     yield loop
     loop.close()