test(02-02): add failing tests for PlatformAdapter base class

- Add test for abstract class instantiation prevention
- Add test for incomplete implementation detection
- Add test for complete implementation instantiation
- Add test for async method signatures
- Add shared fixtures for platform tests

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

tests/test_platforms/test_base.py

@@ -0,0 +1,122 @@
+"""Tests for PlatformAdapter base class
+
+This module tests the interface contracts for the PlatformAdapter abstract base class:
+1. PlatformAdapter is an abstract class and cannot be instantiated directly
+2. Subclasses must implement all abstract methods
+"""
+
+import pytest
+from abc import ABC
+from typing import Dict, Any
+
+from kb_pipeline.platforms.base import PlatformAdapter
+
+
+class TestPlatformAdapterInterface:
+    """Test the PlatformAdapter interface contracts"""
+
+    def test_platform_adapter_is_abstract(self):
+        """Test 1: PlatformAdapter is an abstract class and cannot be instantiated directly"""
+        # Verify it's an ABC subclass
+        assert issubclass(PlatformAdapter, ABC)
+
+        # Verify it cannot be instantiated directly
+        with pytest.raises(TypeError) as exc_info:
+            PlatformAdapter()
+
+        # Error should mention abstract methods
+        assert "abstract" in str(exc_info.value).lower()
+
+    def test_subclass_must_implement_all_methods(self):
+        """Test 2: Subclass must implement all abstract methods"""
+        # Create an incomplete implementation
+        class IncompleteAdapter(PlatformAdapter):
+            def get_content_type(self, url: str) -> str:
+                return "video"
+
+            # Missing: fetch_metadata, fetch_content, get_output_filename
+            # This should fail to instantiate
+
+        with pytest.raises(TypeError) as exc_info:
+            IncompleteAdapter()
+
+        # Verify error mentions missing methods
+        error_msg = str(exc_info.value).lower()
+        assert "abstract" in error_msg or "implement" in error_msg
+
+    def test_complete_implementation_can_be_instantiated(self):
+        """Test that a complete implementation can be instantiated"""
+        class CompleteAdapter(PlatformAdapter):
+            def get_content_type(self, url: str) -> str:
+                return "video"
+
+            async def fetch_metadata(self, content_id: str, content_type: str) -> Dict[str, Any]:
+                return {"title": "test"}
+
+            async def fetch_content(self, content_id: str, content_type: str) -> str:
+                return "# Test Content"
+
+            def get_output_filename(self, content_id: str, content_type: str, suffix: str) -> str:
+                return f"test_{content_id}_{suffix}"
+
+        # Should instantiate without error
+        adapter = CompleteAdapter()
+        assert adapter is not None
+        assert adapter.get_content_type("https://example.com/video/123") == "video"
+
+
+class TestPlatformAdapterMethods:
+    """Test the abstract method signatures"""
+
+    def test_get_content_type_signature(self):
+        """Test get_content_type method signature"""
+        class TestAdapter(PlatformAdapter):
+            def get_content_type(self, url: str) -> str:
+                return "video"
+
+            async def fetch_metadata(self, content_id: str, content_type: str) -> Dict[str, Any]:
+                return {}
+
+            async def fetch_content(self, content_id: str, content_type: str) -> str:
+                return ""
+
+            def get_output_filename(self, content_id: str, content_type: str, suffix: str) -> str:
+                return ""
+
+        adapter = TestAdapter()
+        # Method should accept URL string and return content type string
+        result = adapter.get_content_type("https://www.bilibili.com/video/BV1test")
+        assert isinstance(result, str)
+
+    def test_fetch_metadata_is_async(self):
+        """Test fetch_metadata is an async method"""
+        import inspect
+        assert inspect.iscoroutinefunction(PlatformAdapter.fetch_metadata)
+
+    def test_fetch_content_is_async(self):
+        """Test fetch_content is an async method"""
+        import inspect
+        assert inspect.iscoroutinefunction(PlatformAdapter.fetch_content)
+
+    def test_get_output_filename_signature(self):
+        """Test get_output_filename method signature"""
+        class TestAdapter(PlatformAdapter):
+            def get_content_type(self, url: str) -> str:
+                return ""
+
+            async def fetch_metadata(self, content_id: str, content_type: str) -> Dict[str, Any]:
+                return {}
+
+            async def fetch_content(self, content_id: str, content_type: str) -> str:
+                return ""
+
+            def get_output_filename(self, content_id: str, content_type: str, suffix: str) -> str:
+                return f"{content_type}_{content_id}_{suffix}"
+
+        adapter = TestAdapter()
+        # Method should accept content_id, content_type, suffix and return filename string
+        result = adapter.get_output_filename("BV1test", "video", "metadata.json")
+        assert isinstance(result, str)
+        assert "BV1test" in result
+        assert "video" in result
+        assert "metadata.json" in result