diff --git a/tests/test_activity_sync.py b/tests/test_activity_sync.py
new file mode 100644
index 0000000..688897e
--- /dev/null
+++ b/tests/test_activity_sync.py
@@ -0,0 +1,88 @@
+import pytest
+from unittest.mock import MagicMock, patch
+from datetime import datetime, timedelta
+from stravalib.model import DetailedActivity, ActivityPhotoPrimary
+from freezing.sync.data.activity import ActivitySync
+from freezing.model.orm import Ride, RideEffort, RidePhoto, Athlete
+from freezing.sync.utils.cache import CachingActivityFetcher
+
+@pytest.fixture
+def activity_sync():
+    return ActivitySync()
+
+@pytest.fixture
+def detailed_activity():
+    activity = MagicMock(spec=DetailedActivity)
+    activity.id = 123
+    activity.name = "Test Activity"
+    activity.private = False
+    activity.photo_count = 1
+    activity.start_date_local = datetime.now()
+    activity.distance = MagicMock()
+    activity.distance.num = 1000
+    activity.average_speed = MagicMock()
+    activity.average_speed.num = 10
+    activity.max_speed = MagicMock()
+    activity.max_speed.num = 20
+    activity.elapsed_time = timedelta(hours=1)
+    activity.moving_time = timedelta(hours=1)
+    activity.location_city = "Test City"
+    activity.location_state = "Test State"
+    activity.commute = False
+    activity.trainer = False
+    activity.manual = False
+    activity.total_elevation_gain = MagicMock()
+    activity.total_elevation_gain.num = 100
+    activity.timezone = "UTC"
+    return activity
+
+@pytest.fixture
+def ride():
+    return MagicMock(spec=Ride)
+
+def test_update_ride_basic(activity_sync, detailed_activity, ride):
+    activity_sync.update_ride_basic(detailed_activity, ride)
+    assert ride.name == detailed_activity.name
+    assert ride.private == detailed_activity.private
+    assert ride.start_date == detailed_activity.start_date_local
+    assert ride.distance == 0.621
+    assert ride.average_speed == 22.3694
+    assert ride.maximum_speed == 44.7388
+    assert ride.elapsed_time == detailed_activity.elapsed_time.seconds
+    assert ride.moving_time == detailed_activity.moving_time.seconds
+    assert ride.location == "Test City, Test State"
+    assert ride.commute == detailed_activity.commute
+    assert ride.trainer == detailed_activity.trainer
+    assert ride.manual == detailed_activity.manual
+    assert ride.elevation_gain == 328.084
+    assert ride.timezone == detailed_activity.timezone
+
+def test_write_ride_efforts(activity_sync, detailed_activity, ride):
+    session = MagicMock()
+    detailed_activity.segment_efforts = [
+        MagicMock(id=1, elapsed_time=timedelta(seconds=300), segment=MagicMock(name="Segment 1", id=1)),
+        MagicMock(id=2, elapsed_time=timedelta(seconds=600), segment=MagicMock(name="Segment 2", id=2)),
+    ]
+    with patch("freezing.sync.data.activity.meta.scoped_session", return_value=session):
+        activity_sync.write_ride_efforts(detailed_activity, ride)
+        assert session.add.call_count == 2
+        assert session.flush.call_count == 2
+
+def test_write_ride_photo_primary(activity_sync, detailed_activity, ride):
+    session = MagicMock()
+    primary_photo = MagicMock(spec=ActivityPhotoPrimary)
+    primary_photo.source = 1
+    primary_photo.urls = {"100": "http://example.com/100.jpg", "600": "http://example.com/600.jpg"}
+    detailed_activity.photos.primary = primary_photo
+    with patch("freezing.sync.data.activity.meta.scoped_session", return_value=session):
+        activity_sync.write_ride_photo_primary(detailed_activity, ride)
+        assert session.add.call_count == 1
+        assert session.flush.call_count == 1
+
+def test_update_ride_complete(activity_sync, detailed_activity, ride):
+    session = MagicMock()
+    with patch("freezing.sync.data.activity.meta.scoped_session", return_value=session):
+        activity_sync.update_ride_complete(detailed_activity, ride)
+        assert ride.detail_fetched == True
+        assert session.flush.call_count == 3
+        assert session.commit.call_count == 1