Add automated unit and mock integration test suite

- Configure conftest.py with pytest tmp_path DB isolation fixtures
- Add test_db.py for schema connection validations
- Add test_fetcher.py with mocked yt-dlp subprocess parser checks
- Add test_summarizer.py with mocked transcripts and Claude API requests
- Add test_main.py for FastAPI router endpoints and state updates

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/tests/test_summarizer.py

@@ -0,0 +1,125 @@
+import pytest
+import os
+import httpx
+import aiosqlite
+import summarizer
+from unittest.mock import patch, MagicMock, AsyncMock
+
+class MockTranscript:
+    def fetch(self):
+        return [
+            {"text": "Welcome to this video tutorial.", "start": 0.0, "duration": 3.0},
+            {"text": "Today we are learning about Svelte 5 and runes.", "start": 3.0, "duration": 4.0}
+        ]
+
+class MockTranscriptList:
+    def __init__(self, transcript):
+        self.transcript = transcript
+
+    def find_manually_created_transcript(self, languages):
+        return self.transcript
+
+    def find_generated_transcript(self, languages):
+        return self.transcript
+
+    def __iter__(self):
+        return iter([self.transcript])
+
+@pytest.mark.asyncio
+async def test_download_transcript_success():
+    mock_trans = MockTranscript()
+    mock_list = MockTranscriptList(mock_trans)
+
+    with patch("youtube_transcript_api.YouTubeTranscriptApi.list_transcripts", return_value=mock_list):
+        text = summarizer.download_transcript("test_vid")
+        assert text == "Welcome to this video tutorial. Today we are learning about Svelte 5 and runes."
+
+@pytest.mark.asyncio
+async def test_summarize_video_success(test_db):
+    # Insert a pending video in db first
+    await test_db.execute("""
+        INSERT INTO videos (video_id, title, url, status)
+        VALUES ('summarize_vid', 'Video to Summarize', 'https://www.youtube.com/watch?v=summarize_vid', 'pending')
+    """)
+    await test_db.commit()
+
+    mock_trans = MockTranscript()
+    mock_list = MockTranscriptList(mock_trans)
+
+    # Mock Claude HTTP response
+    mock_response = MagicMock(spec=httpx.Response)
+    mock_response.status_code = 200
+    mock_response.json.return_value = {
+        "content": [
+            {
+                "text": "**Mock Core Hook**\n- Takeaway 1\n- Takeaway 2\nVerdict line."
+            }
+        ]
+    }
+
+    # Patch both transcript api and httpx AsyncClient post call
+    with patch("youtube_transcript_api.YouTubeTranscriptApi.list_transcripts", return_value=mock_list), \
+         patch("httpx.AsyncClient.post", new_callable=AsyncMock, return_value=mock_response) as mock_post:
+
+        summary = await summarizer.summarize_video("summarize_vid")
+
+        # Verify API request details
+        mock_post.assert_called_once()
+        url = mock_post.call_args[0][0]
+        assert "bytecatcode.org" in url
+
+        headers = mock_post.call_args[1]["headers"]
+        assert "x-api-key" in headers
+        assert headers["User-Agent"] is not None
+
+        payload = mock_post.call_args[1]["json"]
+        assert payload["model"] == "claude-haiku-4-5-20251001"
+        assert len(payload["messages"]) == 1
+
+        assert summary == "**Mock Core Hook**\n- Takeaway 1\n- Takeaway 2\nVerdict line."
+
+    # Query db to verify transcript & summary were saved
+    cursor = await test_db.execute("SELECT * FROM videos WHERE video_id = 'summarize_vid'")
+    video = await cursor.fetchone()
+    assert video is not None
+    assert video["transcript"] == "Welcome to this video tutorial. Today we are learning about Svelte 5 and runes."
+    assert video["summary"] == "**Mock Core Hook**\n- Takeaway 1\n- Takeaway 2\nVerdict line."
+
+@pytest.mark.asyncio
+async def test_summarize_all_pending(test_db):
+    # Insert multiple videos, one pending and one already summarized
+    await test_db.execute("""
+        INSERT INTO videos (video_id, title, url, summary, status)
+        VALUES
+        ('pending_vid', 'Pending Video', 'https://youtube.com/watch?v=pending_vid', '', 'pending'),
+        ('done_vid', 'Done Video', 'https://youtube.com/watch?v=done_vid', 'Existing summary', 'pending')
+    """)
+    await test_db.commit()
+
+    mock_trans = MockTranscript()
+    mock_list = MockTranscriptList(mock_trans)
+
+    mock_response = MagicMock(spec=httpx.Response)
+    mock_response.status_code = 200
+    mock_response.json.return_value = {
+        "content": [{"text": "Fresh summary"}]
+    }
+
+    with patch("youtube_transcript_api.YouTubeTranscriptApi.list_transcripts", return_value=mock_list), \
+         patch("httpx.AsyncClient.post", new_callable=AsyncMock, return_value=mock_response) as mock_post:
+
+        await summarizer.summarize_all_pending()
+
+        # Should only call API once for 'pending_vid'
+        mock_post.assert_called_once()
+        payload = mock_post.call_args[1]["json"]
+        assert "Welcome to this video tutorial." in payload["messages"][0]["content"]
+
+    # Verify db states
+    cursor = await test_db.execute("SELECT video_id, summary FROM videos ORDER BY video_id")
+    videos = await cursor.fetchall()
+    assert videos[0]["video_id"] == "done_vid"
+    assert videos[0]["summary"] == "Existing summary" # Untouched
+
+    assert videos[1]["video_id"] == "pending_vid"
+    assert videos[1]["summary"] == "Fresh summary" # Updated