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_fetcher.py

@@ -0,0 +1,112 @@
+import pytest
+import os
+import json
+import aiosqlite
+import fetcher
+import asyncio
+from unittest.mock import patch, AsyncMock
+
+class MockProcess:
+    def __init__(self, stdout_data, returncode=0, stderr_data=b""):
+        self.stdout_data = stdout_data
+        self.stderr_data = stderr_data
+        self.returncode = returncode
+
+    async def communicate(self):
+        return self.stdout_data, self.stderr_data
+
+@pytest.mark.asyncio
+async def test_fetch_subscriptions_no_cookies(tmp_path, monkeypatch):
+    monkeypatch.setattr(fetcher, "COOKIES_PATH", "/non/existent/path/cookies.txt")
+    count = await fetcher.fetch_subscriptions()
+    assert count == 0
+
+@pytest.mark.asyncio
+async def test_fetch_subscriptions_success(test_db, tmp_path, monkeypatch):
+    cookies_file = os.path.join(tmp_path, "mock_cookies.txt")
+    with open(cookies_file, "w") as f:
+        f.write("# Netscape HTTP Cookie File")
+    monkeypatch.setattr(fetcher, "COOKIES_PATH", cookies_file)
+
+    video1 = {
+        "id": "vid123",
+        "title": "Mock Video 1",
+        "uploader": "Uploader One",
+        "uploader_id": "chan123",
+        "upload_date": "20260601",
+        "duration": 360,
+        "thumbnail": "https://img.youtube.com/vi/vid123/hqdefault.jpg"
+    }
+    video2 = {
+        "id": "vid456",
+        "title": "Mock Video 2",
+        "uploader": "Uploader Two",
+        "uploader_id": "chan456",
+        "upload_date": "20260602",
+        "duration": 720
+    }
+    stdout_bytes = (json.dumps(video1) + "\n" + json.dumps(video2) + "\n").encode("utf-8")
+
+    mock_process = MockProcess(stdout_data=stdout_bytes, returncode=0)
+
+    with patch("asyncio.create_subprocess_exec", return_value=mock_process) as mock_exec:
+        count = await fetcher.fetch_subscriptions()
+
+        mock_exec.assert_called_once()
+        args = mock_exec.call_args[0]
+        assert "yt-dlp" in args
+        assert "https://www.youtube.com/feed/subscriptions" in args
+        assert cookies_file in args
+        assert count == 2
+
+    # Query db to verify values
+    cursor = await test_db.execute("SELECT * FROM videos ORDER BY video_id")
+    videos = await cursor.fetchall()
+    assert len(videos) == 2
+
+    assert videos[0]["video_id"] == "vid123"
+    assert videos[0]["title"] == "Mock Video 1"
+    assert videos[0]["channel_name"] == "Uploader One"
+    assert videos[0]["channel_id"] == "chan123"
+    assert videos[0]["url"] == "https://www.youtube.com/watch?v=vid123"
+    assert videos[0]["thumbnail_url"] == "https://img.youtube.com/vi/vid123/hqdefault.jpg"
+    assert videos[0]["publish_date"] == "2026-06-01"
+    assert videos[0]["duration"] == 360
+    assert videos[0]["status"] == "pending"
+
+    assert videos[1]["video_id"] == "vid456"
+    assert videos[1]["title"] == "Mock Video 2"
+    assert videos[1]["publish_date"] == "2026-06-02"
+    assert videos[1]["duration"] == 720
+
+@pytest.mark.asyncio
+async def test_fetch_subscriptions_skip_duplicates(test_db, tmp_path, monkeypatch):
+    cookies_file = os.path.join(tmp_path, "mock_cookies.txt")
+    with open(cookies_file, "w") as f:
+        f.write("# Netscape HTTP Cookie File")
+    monkeypatch.setattr(fetcher, "COOKIES_PATH", cookies_file)
+
+    # Insert an existing video record first
+    await test_db.execute("""
+        INSERT INTO videos (video_id, title, url, status)
+        VALUES ('vid123', 'Mock Video 1', 'https://www.youtube.com/watch?v=vid123', 'pending')
+    """)
+    await test_db.commit()
+
+    video1 = {
+        "id": "vid123",
+        "title": "Mock Video 1",
+        "upload_date": "20260601"
+    }
+    video2 = {
+        "id": "vid456",
+        "title": "Mock Video 2",
+        "upload_date": "20260602"
+    }
+    stdout_bytes = (json.dumps(video1) + "\n" + json.dumps(video2) + "\n").encode("utf-8")
+
+    mock_process = MockProcess(stdout_data=stdout_bytes, returncode=0)
+
+    with patch("asyncio.create_subprocess_exec", return_value=mock_process):
+        count = await fetcher.fetch_subscriptions()
+        assert count == 1 # Only 1 new video should be added (vid456)