diff --git a/tests/test_sync.py b/tests/test_sync.py
index 4b18751..6f12640 100644
--- a/tests/test_sync.py
+++ b/tests/test_sync.py
@@ -41,5 +41,81 @@ def test_start_stop_server(sync_protocol):
 
 def test_sync_with_peer_no_connection(sync_protocol, db):
     """Test sync with unreachable peer."""
-    synced = sync_protocol.sync_with_peer("127.0.0.1", 9999)
-    assert synced == 0
+    peer = {"host": "127.0.0.1", "port": 9999, "peer_id": "test"}
+    result = sync_protocol.sync_with_peer(peer)
+    assert result["status"] == "error"
+
+
+def test_get_all_snippets_for_sync(db):
+    """Test getting all snippets for sync."""
+    db.add_snippet(title="Test 1", code="code1")
+    db.add_snippet(title="Test 2", code="code2")
+    
+    snippets = db.export_all()
+    assert len(snippets) == 2
+
+
+def test_get_snippets_since_timestamp(db):
+    """Test getting snippets updated since timestamp."""
+    from datetime import datetime, timedelta
+    
+    db.add_snippet(title="Old", code="old code")
+    old_time = datetime.utcnow().isoformat()
+    
+    db.add_snippet(title="New", code="new code")
+    
+    snippets = db.list_snippets(limit=100)
+    old_snippets = [s for s in snippets if s["updated_at"] <= old_time]
+    new_snippets = [s for s in snippets if s["updated_at"] > old_time]
+    
+    assert len(old_snippets) >= 1
+    assert len(new_snippets) >= 1
+
+
+def test_upsert_snippet(db):
+    """Test upserting a snippet."""
+    snippet_id = db.add_snippet(title="Original", code="original")
+    assert snippet_id > 0
+    
+    result = db.import_snippet({"title": "Original", "code": "updated"}, strategy="replace")
+    assert result == -1
+    
+    snippet = db.get_snippet(snippet_id)
+    assert snippet["code"] == "updated"
+
+
+def test_update_sync_meta(db):
+    """Test updating sync metadata."""
+    from datetime import datetime
+    
+    db.add_peer("peer1", "localhost", 8765)
+    db.update_sync_meta("peer1", datetime.utcnow().isoformat())
+    
+    peers = db.list_sync_peers()
+    assert len(peers) == 1
+    assert peers[0]["last_sync"] is not None
+
+
+def test_discovery_service_init():
+    """Test discovery service initialization."""
+    from snip.sync.discovery import DiscoveryService
+    
+    discovery = DiscoveryService(port=18765)
+    assert discovery.port == 18765
+
+
+def test_peer_cache_persistence(tmp_path):
+    """Test peer cache persistence."""
+    from snip.sync.discovery import DiscoveryService
+    import json
+    
+    cache_file = tmp_path / "peers.json"
+    discovery = DiscoveryService()
+    discovery._peer_cache_file = cache_file
+    
+    peers = [{"peer_id": "test", "host": "localhost", "port": 8765}]
+    discovery.save_peer_cache(peers)
+    
+    loaded = discovery.load_peer_cache()
+    assert len(loaded) == 1
+    assert loaded[0]["peer_id"] == "test"
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