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_main.py

@@ -0,0 +1,107 @@
+import pytest
+from fastapi.testclient import TestClient
+from main import app, get_db
+import aiosqlite
+from unittest.mock import patch
+
+@pytest.fixture
+def client(test_db):
+    # Override get_db dependency to use the isolated test database
+    async def override_get_db():
+        yield test_db
+    app.dependency_overrides[get_db] = override_get_db
+    yield TestClient(app)
+    app.dependency_overrides.clear()
+
+def test_health(client):
+    response = client.get("/api/health")
+    assert response.status_code == 200
+    assert response.json() == {"status": "ok"}
+
+@pytest.mark.asyncio
+async def test_get_videos(client, test_db):
+    # Insert mock videos with different statuses
+    await test_db.execute("""
+        INSERT INTO videos (video_id, title, url, status)
+        VALUES
+        ('v1', 'Pending Video', 'https://youtube.com/v1', 'pending'),
+        ('v2', 'Read Video', 'https://youtube.com/v2', 'read'),
+        ('v3', 'Skipped Video', 'https://youtube.com/v3', 'skipped')
+    """)
+    await test_db.commit()
+
+    # Test pending filter
+    resp = client.get("/api/videos?status=pending")
+    assert resp.status_code == 200
+    data = resp.json()
+    assert len(data) == 1
+    assert data[0]["video_id"] == "v1"
+
+    # Test read filter
+    resp = client.get("/api/videos?status=read")
+    assert resp.status_code == 200
+    data = resp.json()
+    assert len(data) == 1
+    assert data[0]["video_id"] == "v2"
+
+def test_update_status_success(client, test_db):
+    # Insert pending video
+    test_db.execute_insert = lambda *args: None # Helper since we execute raw
+    async def insert():
+        await test_db.execute("""
+            INSERT INTO videos (video_id, title, url, status)
+            VALUES ('status_vid', 'Title', 'https://youtube.com/watch?v=status_vid', 'pending')
+        """)
+        await test_db.commit()
+
+    import asyncio
+    asyncio.run(insert())
+
+    # Send status update
+    resp = client.post("/api/videos/status_vid/status", json={"status": "read"})
+    assert resp.status_code == 200
+    assert resp.json() == {"message": "Video status_vid status updated to read."}
+
+    # Verify db was updated
+    async def verify():
+        cursor = await test_db.execute("SELECT status FROM videos WHERE video_id = 'status_vid'")
+        row = await cursor.fetchone()
+        return row["status"]
+
+    status = asyncio.run(verify())
+    assert status == "read"
+
+def test_update_status_invalid_value(client):
+    resp = client.post("/api/videos/status_vid/status", json={"status": "archived"})
+    assert resp.status_code == 400
+    assert "Invalid status value" in resp.json()["detail"]
+
+def test_update_status_not_found(client):
+    resp = client.post("/api/videos/missing_vid/status", json={"status": "read"})
+    assert resp.status_code == 404
+    assert "Video not found" in resp.json()["detail"]
+
+def test_trigger_fetch(client):
+    with patch("main.bg_fetch_and_summarize") as mock_task:
+        resp = client.post("/api/videos/fetch")
+        assert resp.status_code == 200
+        assert "sync and summarization running in background" in resp.json()["message"]
+
+@pytest.mark.asyncio
+async def test_trigger_summarize(client, test_db):
+    # Insert video
+    await test_db.execute("""
+        INSERT INTO videos (video_id, title, url, status)
+        VALUES ('sum_vid', 'Title', 'https://youtube.com/watch?v=sum_vid', 'pending')
+    """)
+    await test_db.commit()
+
+    with patch("main.summarize_video") as mock_sum:
+        resp = client.post("/api/videos/sum_vid/summarize")
+        assert resp.status_code == 200
+        assert "summarization for video sum_vid queued" in resp.json()["message"].lower()
+
+def test_trigger_summarize_not_found(client):
+    resp = client.post("/api/videos/missing_sum/summarize")
+    assert resp.status_code == 404
+    assert "Video not found" in resp.json()["detail"]