private async Task ClearLandmark(int id, Landmark linkedObject = null)
        {
            var landmarks = CreateMockLandmarkDbSet();
            var context = CreateMockLocationContext(landmarks: landmarks.Object);

            var service = new LocationService(context.Object);

            await service.ClearLandmark(id);

            if (linkedObject != null)
            {
                Assert.True((linkedObject.Expiry - DateTimeOffset.Now).TotalSeconds < -DateTimeTolerance);
                context.Verify(c => c.SaveChangesAsync());
            }
            else
            {
                context.Verify(c => c.SaveChangesAsync(), Times.Never);
            }
        }