public void AddFriends_AddFriendsModelToPackage_ReturnFriends() { //arrange Package package = _data.GetCustomPackage(); package.Friends = null; _mock.Setup(s => s.Package.Get(It.IsAny <int>())) .Returns(package); _mock.Setup(s => s.Package.GetPackageWithFriends(It.IsAny <int>())) .Returns(_data.GetCustomPackage()); _manager = new PackageManager(_mock.Object); //act var res = _manager.AddFriends(1, _data.GetFriends()); //assert Assert.IsNotNull(res); }