public void CheckIfNewCustomerAdded()
{
Mock <ICustomerRepository> repositoryMock = new Mock <ICustomerRepository>();
ShopService ss = new ShopService(repositoryMock.Object);
Customer customer = ss.CreateNewCustomer("Marko Golovko", "*****@*****.**");
repositoryMock.Verify(k => k.Insert(customer), Times.Once());
}