test: migrate backend suites to pytest with module coverage gate

Split backend tests into unit and integration suites, add isolated fixtures and coverage enforcement, and update CI and test documentation. Cover current authentication, content, notification, payment, media, and admin flows; fix behaviors revealed by the new tests. Validate both suites and the per-module gate against local PostgreSQL.

apps/notifications/tests/integration/test_redis_store.py

@@ -0,0 +1,38 @@
+from datetime import timedelta
+
+import pytest
+from django.utils import timezone
+
+from apps.notifications import services
+
+
+pytestmark = pytest.mark.integration
+
+
+def test_fake_redis_store_add_filter_mark_and_delete(fake_notification_redis, monkeypatch):
+    monkeypatch.setattr(services, "redis_client", fake_notification_redis)
+    first = services.RedisNotificationStore.add("user-1", {"type": "news", "title": "One", "body_markdown": "# Long body"})
+    second = services.RedisNotificationStore.add("user-1", {"type": "event", "title": "Two"})
+    assert services.RedisNotificationStore.unread_count("user-1") == 2
+    assert services.RedisNotificationStore.list("user-1", type_filter="news")[1] == 1
+    assert services.RedisNotificationStore.get("user-2", first["id"]) is None
+    marked = services.RedisNotificationStore.mark_seen("user-1", first["id"])
+    assert marked["unread_count"] == 1
+    assert services.RedisNotificationStore.list("user-1", read_filter="read")[1] == 1
+    assert services.RedisNotificationStore.mark_all_seen("user-1") == 2
+    assert services.RedisNotificationStore.unread_count("user-1") == 0
+    assert services.RedisNotificationStore.delete("user-1", second["id"])
+    assert not services.RedisNotificationStore.delete("user-1", second["id"])
+    assert services.RedisNotificationStore.get("user-1", second["id"]) is None
+
+
+def test_fake_redis_store_cleans_expired_and_corrupt_records(fake_notification_redis, monkeypatch):
+    monkeypatch.setattr(services, "redis_client", fake_notification_redis)
+    old = (timezone.now() - timedelta(days=90)).isoformat()
+    expired = services.RedisNotificationStore.add("user-1", {"created_at": old, "title": "Old"})
+    recent = services.RedisNotificationStore.add("user-1", {"title": "Recent"})
+    assert services.RedisNotificationStore.cleanup_expired(retention_days=30) == 1
+    assert services.RedisNotificationStore.get("user-1", expired["id"]) is None
+    fake_notification_redis.hset(services.RedisNotificationStore._data_key("user-1"), recent["id"], "broken json")
+    assert services.RedisNotificationStore.list("user-1") == ([], 0)
+    assert services.RedisNotificationStore.get("user-1", recent["id"]) is None