public void CanEnrollACustomer()
 {
     //Arrange
     FakeCustomerValidator validation = new FakeCustomerValidator();
     FakeCreditCheckValidator creditCheck = new FakeCreditCheckValidator();
     FakeCustomerRepository repository= new FakeCustomerRepository();
     var sut = new CustomerService(validation, creditCheck, repository);
     Customer customer = new Customer();
     //Act
     sut.EnrollCustomer(customer);
     //Assert
     Assert.That(validation.WasCalled);
     Assert.That(creditCheck.WasCalled);
     Assert.That(repository.WasCalled);
 }