public void TestGetListOfChildrenWithParent()
        {
            var customerManagerMock = new Mock <ICustomerManager>();

            customerManagerMock.Setup(m =>
                                      m.GetAllCustomers())
            .Returns(
                new List <Customer>
            {
                new Customer {
                    CustomerID = 1, Name = "Adam", Address = "Örebro", Borrows = new List <Borrow> {
                        new Borrow {
                            DateOfBorrow = new DateTime(2018, 10, 10), Book = new Book {
                            }
                        }
                    }
                },
                new Customer {
                    CustomerID = 2, Parent = new Customer {
                        CustomerID = 9
                    }
                },
                new Customer {
                    CustomerID = 3, Parent = new Customer {
                        CustomerID = 10
                    }
                },
                new Customer {
                    CustomerID = 4, Parent = new Customer {
                        CustomerID = 11
                    }
                },
                new Customer {
                    CustomerID = 5, Parent = new Customer {
                        CustomerID = 12
                    }
                },
                new Customer {
                    CustomerID = 6, Parent = new Customer {
                        CustomerID = 13
                    }
                },
                new Customer {
                    CustomerID = 7, Parent = new Customer {
                        CustomerID = 14
                    }
                },
                new Customer {
                    CustomerID = 8, Parent = new Customer {
                        CustomerID = 15
                    }
                }
            });



            var customerAPI  = new CustomerAPI(customerManagerMock.Object, null, null);
            var childrenList = customerAPI.GetListOfChildrenWithParentAdressForChildrenEvent();

            Assert.AreEqual(3, childrenList.Count);
        }