test: add notifications integration behavior guard

surfsense_backend/tests/integration/notifications/test_mention_handler.py

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+"""Behavior guard for the @mention notification handler."""
+
+from __future__ import annotations
+
+import pytest
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.db import SearchSpace, User
+from app.notifications.service import NotificationService
+
+pytestmark = pytest.mark.integration
+
+handler = NotificationService.mention
+
+
+async def _notify(db_session, db_user, db_search_space, *, mention_id=1, preview="hi"):
+    """Raise an @mention notification for the assertions in the tests below."""
+    return await handler.notify_new_mention(
+        session=db_session,
+        mentioned_user_id=db_user.id,
+        mention_id=mention_id,
+        comment_id=10,
+        message_id=20,
+        thread_id=30,
+        thread_title="Thread",
+        author_id="author-1",
+        author_name="Alice",
+        author_avatar_url=None,
+        author_email="alice@surfsense.net",
+        content_preview=preview,
+        search_space_id=db_search_space.id,
+    )
+
+
+async def test_new_mention_title_and_message(
+    db_session: AsyncSession, db_user: User, db_search_space: SearchSpace
+):
+    """A mention notification names the author and carries the comment preview."""
+    notification = await _notify(db_session, db_user, db_search_space, preview="hello")
+
+    assert notification.type == "new_mention"
+    assert notification.title == "Alice mentioned you"
+    assert notification.message == "hello"
+
+
+async def test_new_mention_truncates_long_preview(
+    db_session: AsyncSession, db_user: User, db_search_space: SearchSpace
+):
+    """A long comment preview is truncated in the mention message."""
+    notification = await _notify(db_session, db_user, db_search_space, preview="x" * 150)
+
+    assert notification.message == "x" * 100 + "..."
+
+
+async def test_new_mention_is_idempotent(
+    db_session: AsyncSession, db_user: User, db_search_space: SearchSpace
+):
+    """Re-notifying the same mention id reuses the existing notification row."""
+    first = await _notify(db_session, db_user, db_search_space, mention_id=7)
+    second = await _notify(db_session, db_user, db_search_space, mention_id=7)
+
+    assert second.id == first.id