How to properly mock void methods in Mockito?

Hi everyone! I'm a beginner Java developer writing unit tests using Mockito. I've encountered a problem: I can't figure out how to properly mock a method that returns nothing (void).

Here's a simple example. There's a class UserService that sends an email via EmailService:

public class EmailService {\n    public void sendEmail(String to, String subject, String body) {\n        // actual email sending\n        System.out.println("Email sent to " + to);\n    }\n}\n\npublic class UserService {\n    private final EmailService emailService;\n    \n    public UserService(EmailService emailService) {\n        this.emailService = emailService;\n    }\n    \n    public void registerUser(String email) {\n        // some registration logic