diff --git a/backend/tests/test_chat_memory.py b/backend/tests/test_chat_memory.py
new file mode 100644
index 0000000..dd42dab
--- /dev/null
+++ b/backend/tests/test_chat_memory.py
@@ -0,0 +1,95 @@
+from pathlib import Path
+import tempfile
+import unittest
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+
+from backend.chat_memory import (
+    build_chat_memory_context,
+    ensure_chat_memory_schema,
+    sync_all_chat_memory,
+    sync_chat_memory_for_session,
+)
+from backend.database import Base
+from backend.models import ChatMessage, ChatSession
+
+
+class ChatMemoryTests(unittest.TestCase):
+    def setUp(self):
+        self.temp = tempfile.TemporaryDirectory()
+        self.engine = create_engine(
+            f"sqlite:///{Path(self.temp.name) / 'memory.db'}",
+            connect_args={"check_same_thread": False},
+        )
+        Base.metadata.create_all(self.engine)
+        ensure_chat_memory_schema(self.engine)
+        self.Session = sessionmaker(bind=self.engine)
+
+    def tearDown(self):
+        self.engine.dispose()
+        self.temp.cleanup()
+
+    def _turn(self, db, session_id, title, user_content, assistant_content):
+        session = ChatSession(session_id=session_id, name=title)
+        db.add(session)
+        db.flush()
+        db.add(ChatMessage(session_pk=session.id, role="user", content=user_content))
+        db.flush()
+        db.add(ChatMessage(session_pk=session.id, role="assistant", content=assistant_content))
+        db.flush()
+        return session
+
+    def test_retrieves_completed_past_turns(self):
+        db = self.Session()
+        try:
+            self._turn(
+                db,
+                "past",
+                "Tauri Packaging",
+                "What did we decide about mac packaging?",
+                "Use the PyInstaller backend sidecar and keep app data outside the bundle.",
+            )
+            db.commit()
+            sync_all_chat_memory(db)
+
+            context = build_chat_memory_context(db, "remind me about the backend sidecar packaging plan")
+        finally:
+            db.close()
+
+        self.assertIn("chat_memory_context", context["context_block"])
+        self.assertIn("PyInstaller backend sidecar", context["context_block"])
+        self.assertEqual(context["sources"][0]["source_session_id"], "past")
+
+    def test_excludes_active_session(self):
+        db = self.Session()
+        try:
+            self._turn(db, "current", "Current", "secret kiwi topic", "Only the current chat mentions kiwi.")
+            db.commit()
+            sync_all_chat_memory(db)
+
+            excluded = build_chat_memory_context(db, "kiwi topic", exclude_session_id="current")
+            included = build_chat_memory_context(db, "kiwi topic")
+        finally:
+            db.close()
+
+        self.assertEqual(excluded["context_block"], "")
+        self.assertIn("kiwi", included["context_block"])
+
+    def test_resync_removes_stale_turn_content(self):
+        db = self.Session()
+        try:
+            session = self._turn(db, "past", "Old Decision", "backend sidecar", "Keep using the old sidecar plan.")
+            db.commit()
+            sync_all_chat_memory(db)
+
+            assistant = db.query(ChatMessage).filter(ChatMessage.role == "assistant").one()
+            assistant.content = "This turn now discusses an unrelated renderer detail."
+            db.commit()
+            sync_chat_memory_for_session(db, session.session_id)
+
+            context = build_chat_memory_context(db, "old sidecar plan")
+        finally:
+            db.close()
+
+        self.assertEqual(context["context_block"], "")