test(02-02): add article content tests with YAML frontmatter

- Add test for article content returning Markdown format
- Add test for YAML frontmatter with required fields
- Add test for video content returning empty (ASR handling)
- Add test for unsupported content type error

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

tests/test_platforms/test_bilibili.py

@@ -179,3 +179,73 @@ class TestBilibiliAdapterArticleMetadata:
             await adapter.fetch_metadata("test123", "unknown")
 
         assert "Unsupported content type" in str(exc_info.value)
+
+
+class TestBilibiliAdapterArticleContent:
+    """Test article content extraction (Task 3)"""
+
+    @pytest.mark.asyncio
+    async def test_fetch_article_content_returns_markdown(self, mock_article_metadata, mock_article_content, mock_state_manager):
+        """Test 2: fetch_content("cvxxx", "article") returns Markdown format content"""
+        adapter = BilibiliAdapter(state_manager=mock_state_manager)
+
+        with patch.object(adapter, '_extractor') as mock_extractor:
+            mock_extractor.extract_article_metadata.return_value = mock_article_metadata
+
+            # Mock the internal _fetch_article_content method
+            with patch.object(adapter, '_fetch_article_content', return_value=mock_article_content):
+                result = await adapter.fetch_content("cv12345678", "article")
+
+                # Should return a non-empty string
+                assert result is not None
+                assert len(result) > 0
+                # Should contain the content
+                assert "Test Article Title" in result or "article" in result.lower()
+
+    @pytest.mark.asyncio
+    async def test_fetch_article_content_has_yaml_frontmatter(self, mock_article_metadata, mock_article_content, mock_state_manager):
+        """Test 3: Markdown includes YAML Frontmatter with required fields"""
+        adapter = BilibiliAdapter(state_manager=mock_state_manager)
+
+        with patch.object(adapter, '_extractor') as mock_extractor:
+            mock_extractor.extract_article_metadata.return_value = mock_article_metadata
+
+            with patch.object(adapter, '_fetch_article_content', return_value=mock_article_content):
+                result = await adapter.fetch_content("cv12345678", "article")
+
+                # Check YAML frontmatter structure
+                assert result.startswith("---\n"), "Content should start with YAML frontmatter"
+
+                # Check required fields in frontmatter
+                assert "title:" in result
+                assert "author:" in result
+                assert "source_url:" in result
+                assert "platform:" in result
+                assert "content_type:" in result
+                assert "fetched_at:" in result
+
+                # Check specific values
+                assert "Test Article Title" in result
+                assert "Test Author" in result
+                assert "bilibili" in result
+                assert "https://www.bilibili.com/read/cv12345678" in result
+
+    @pytest.mark.asyncio
+    async def test_fetch_video_content_returns_empty(self, mock_state_manager):
+        """Test that fetch_content for video returns empty string (handled by ASR)"""
+        adapter = BilibiliAdapter(state_manager=mock_state_manager)
+
+        result = await adapter.fetch_content("BV1test12345", "video")
+
+        # Video content should return empty string (handled by ASR in Phase 3)
+        assert result == ""
+
+    @pytest.mark.asyncio
+    async def test_fetch_content_unsupported_type_raises_error(self, mock_state_manager):
+        """Test that fetch_content with unsupported type raises ValueError"""
+        adapter = BilibiliAdapter(state_manager=mock_state_manager)
+
+        with pytest.raises(ValueError) as exc_info:
+            await adapter.fetch_content("test123", "unknown")
+
+        assert "Unsupported content type" in str(exc_info.value)