test(04-02): add failing tests for DownloadProcessor metadata fetching

TDD RED phase:
- Test DownloadProcessor fetches Bilibili video metadata correctly
- Test DownloadProcessor fetches Zhihu answer metadata correctly
- Test DownloadProcessor records state on success
- Test DownloadProcessor records state on failure

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_processors/test_download.py

@@ -125,3 +125,189 @@ class TestDownloadOutputSchema:
         )
         assert output.success is False
         assert output.error_message == "Network error"
+
+
+class TestDownloadProcessorMetadata:
+    """Tests for DownloadProcessor metadata fetching."""
+
+    @pytest.fixture
+    def mock_bilibili_adapter(self):
+        """Create a mock BilibiliAdapter."""
+        adapter = MagicMock()
+        adapter.fetch_metadata = AsyncMock(return_value={
+            "metadata": {
+                "title": "Test Video Title",
+                "mid": 12345,
+                "bvid": "BV1xx",
+            },
+            "stats": {
+                "view": 1000,
+                "like": 100,
+            },
+            "description": "Test description"
+        })
+        adapter.get_output_filename = MagicMock(
+            return_value="bilibili_BV1xx_metadata.json"
+        )
+        return adapter
+
+    @pytest.fixture
+    def mock_zhihu_adapter(self):
+        """Create a mock ZhihuAdapter."""
+        adapter = MagicMock()
+        adapter.fetch_metadata = AsyncMock(return_value={
+            "title": "Test Answer Title",
+            "author": "Test Author",
+            "url": "https://www.zhihu.com/question/123/answer/456",
+            "content_markdown": "Test content"
+        })
+        adapter.get_output_filename = MagicMock(
+            return_value="zhihu_456_metadata.json"
+        )
+        return adapter
+
+    @pytest.fixture
+    def mock_state_manager(self):
+        """Create a mock WorkflowStateManager."""
+        manager = MagicMock()
+        manager.load = MagicMock(return_value=None)
+        manager.save = MagicMock()
+        return manager
+
+    @pytest.mark.asyncio
+    async def test_metadata_fetches_bilibili_video_metadata_correctly(
+        self, mock_bilibili_adapter, mock_state_manager, tmp_path
+    ):
+        """Test 1: DownloadProcessor fetches Bilibili video metadata correctly"""
+        from kb_pipeline.processors.download import DownloadProcessor
+        from kb_pipeline.schemas import DownloadInput
+
+        input_data = DownloadInput(
+            content_id="BV1xx",
+            platform="bilibili",
+            content_dir=str(tmp_path),
+            content_type="video"
+        )
+
+        with patch.object(
+            DownloadProcessor, '_get_adapter', return_value=mock_bilibili_adapter
+        ):
+            processor = DownloadProcessor(state_manager=mock_state_manager)
+            result = await processor.process(input_data)
+
+        assert result.success is True
+        assert result.title == "Test Video Title"
+        assert "bilibili_BV1xx_metadata.json" in result.metadata_file
+
+        # Verify adapter was called correctly
+        mock_bilibili_adapter.fetch_metadata.assert_called_once_with(
+            "BV1xx", "video"
+        )
+
+    @pytest.mark.asyncio
+    async def test_metadata_fetches_zhihu_answer_metadata_correctly(
+        self, mock_zhihu_adapter, mock_state_manager, tmp_path
+    ):
+        """Test 2: DownloadProcessor fetches Zhihu answer metadata correctly"""
+        from kb_pipeline.processors.download import DownloadProcessor
+        from kb_pipeline.schemas import DownloadInput
+
+        input_data = DownloadInput(
+            content_id="456",
+            platform="zhihu",
+            content_dir=str(tmp_path),
+            content_type="answer"
+        )
+
+        with patch.object(
+            DownloadProcessor, '_get_adapter', return_value=mock_zhihu_adapter
+        ):
+            processor = DownloadProcessor(state_manager=mock_state_manager)
+            result = await processor.process(input_data)
+
+        assert result.success is True
+        assert result.title == "Test Answer Title"
+
+        # Verify adapter was called correctly
+        mock_zhihu_adapter.fetch_metadata.assert_called_once_with(
+            "456", "answer"
+        )
+
+    @pytest.mark.asyncio
+    async def test_metadata_records_state_on_success(
+        self, mock_bilibili_adapter, mock_state_manager, tmp_path
+    ):
+        """Test 3: DownloadProcessor records state on success"""
+        from kb_pipeline.processors.download import DownloadProcessor
+        from kb_pipeline.schemas import DownloadInput, WorkflowState
+
+        # Create a mock state that will be updated
+        mock_state = MagicMock(spec=WorkflowState)
+        mock_state.is_step_completed = MagicMock(return_value=False)
+        mock_state_manager.load.return_value = mock_state
+
+        input_data = DownloadInput(
+            content_id="BV1xx",
+            platform="bilibili",
+            content_dir=str(tmp_path),
+            content_type="video"
+        )
+
+        with patch.object(
+            DownloadProcessor, '_get_adapter', return_value=mock_bilibili_adapter
+        ):
+            processor = DownloadProcessor(state_manager=mock_state_manager)
+            result = await processor.process(input_data)
+
+        assert result.success is True
+
+        # Verify state was recorded
+        mock_state.mark_step_completed.assert_called_once()
+        call_args = mock_state.mark_step_completed.call_args
+        assert call_args[0][0] == "download"  # step_name
+        mock_state_manager.save.assert_called_once_with(mock_state)
+
+    @pytest.mark.asyncio
+    async def test_metadata_records_state_on_failure(
+        self, mock_bilibili_adapter, mock_state_manager, tmp_path
+    ):
+        """Test 4: DownloadProcessor records state on failure"""
+        from kb_pipeline.processors.download import DownloadProcessor
+        from kb_pipeline.schemas import DownloadInput, WorkflowState
+        from kb_pipeline.errors import NetworkError
+
+        # Make adapter raise an error
+        mock_bilibili_adapter.fetch_metadata = AsyncMock(
+            side_effect=NetworkError(
+                step_name="download",
+                input_summary="BV1xx",
+                cause=Exception("Network timeout")
+            )
+        )
+
+        # Create a mock state that will be updated
+        mock_state = MagicMock(spec=WorkflowState)
+        mock_state.is_step_completed = MagicMock(return_value=False)
+        mock_state_manager.load.return_value = mock_state
+
+        input_data = DownloadInput(
+            content_id="BV1xx",
+            platform="bilibili",
+            content_dir=str(tmp_path),
+            content_type="video"
+        )
+
+        with patch.object(
+            DownloadProcessor, '_get_adapter', return_value=mock_bilibili_adapter
+        ):
+            processor = DownloadProcessor(state_manager=mock_state_manager)
+            result = await processor.process(input_data)
+
+        assert result.success is False
+        assert "Network timeout" in result.error_message
+
+        # Verify failure was recorded
+        mock_state.mark_step_failed.assert_called_once()
+        call_args = mock_state.mark_step_failed.call_args
+        assert call_args[0][0] == "download"  # step_name
+        mock_state_manager.save.assert_called_once_with(mock_state)