For demo purposes: https://www.alexjamesbrown.com/blog/development/better-assertions-when-verifying-moqd-methods-have-been-called/

CustomerController.cs

public class CustomerController : Controller
{
    private ICustomerService _customerService;
 
    public CustomerController(ICustomerService customerService)
    {
        _customerService = customerService;
    }
 
    public IActionResult Post(string firstName, string lastName)
    {
        var customer = new Customer
        {
            FirstName = firstName,
            LastName = lastName
        };
 
        var customerId = customerService.Save(customer);
 
        return Created("/customer/" + customerId, customer);
    }
}