feat(gateway): NatsWriteConsumer (Core NATS, queue group) (C2)

tests/unit/adapters/test_nats_consumer.py

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+import json
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from ingestor.adapters.nats_consumer import NatsWriteConsumer
+
+
+def make_consumer(**kwargs):
+    return NatsWriteConsumer(
+        nats_url='nats://localhost:4222',
+        write_engine=AsyncMock(),
+        logger=MagicMock(),
+        **kwargs,
+    )
+
+
+@pytest.mark.asyncio
+async def test_handle_valid_json_dispatches_to_write_engine():
+    consumer = make_consumer()
+    payload = {'server_id': 'srv1', 'addr': 'ns=2;i=5', 'value': 1.0, 'data_type': 'float'}
+    msg = MagicMock(data=json.dumps(payload).encode())
+
+    await consumer._handle(msg)
+
+    consumer.write_engine.write.assert_awaited_once_with(payload)
+
+
+@pytest.mark.asyncio
+async def test_handle_invalid_json_drops_message_and_logs_error():
+    consumer = make_consumer()
+    msg = MagicMock(data=b'not-json')
+
+    await consumer._handle(msg)
+
+    consumer.write_engine.write.assert_not_awaited()
+    consumer.logger.error.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_start_subscribes_with_subject_and_queue():
+    consumer = make_consumer(subject='opc.write', queue='gateway-writers')
+    mock_nc = AsyncMock()
+    mock_nc.subscribe = AsyncMock()
+
+    with patch('ingestor.adapters.nats_consumer.nats') as mock_nats:
+        mock_nats.connect = AsyncMock(return_value=mock_nc)
+        await consumer.start()
+
+    mock_nats.connect.assert_awaited_once_with(servers='nats://localhost:4222')
+    mock_nc.subscribe.assert_awaited_once_with(
+        'opc.write', queue='gateway-writers', cb=consumer._handle
+    )
+
+
+@pytest.mark.asyncio
+async def test_stop_before_start_does_not_raise():
+    consumer = make_consumer()
+
+    await consumer.stop()  # no raise
+
+
+@pytest.mark.asyncio
+async def test_stop_after_start_drains_and_unsubscribes():
+    consumer = make_consumer()
+    mock_nc = AsyncMock()
+    mock_sub = AsyncMock()
+    mock_nc.subscribe = AsyncMock(return_value=mock_sub)
+
+    with patch('ingestor.adapters.nats_consumer.nats') as mock_nats:
+        mock_nats.connect = AsyncMock(return_value=mock_nc)
+        await consumer.start()
+        await consumer.stop()
+
+    mock_sub.unsubscribe.assert_awaited_once()
+    mock_nc.drain.assert_awaited_once()