Injecting MailClient in while testing in Spring Boot - spring

Question

I have this classes that runs well when I run the app.
#Service("bookManager")
public class BookManagerImpl implements BookManager {
private MailClient mailClient;
..
}
#Service
public class MailClient {
protected static final Logger looger = LoggerFactory.getLogger(MailClient.class);
#Autowired
private JavaMailSender mailSender;
private MailContentBuilder mailContentBuilder;
#Autowired
public MailClient(JavaMailSender mailSender, MailContentBuilder mailContentBuilder) {
this.mailSender = mailSender;
this.mailContentBuilder = mailContentBuilder;
}
//TODO: in a properties
public void prepareAndSend(String recipient, String message) {
MimeMessagePreparator messagePreparator = mimeMessage -> {
MimeMessageHelper messageHelper = new MimeMessageHelper(mimeMessage);
messageHelper.setFrom("nunito#calzada.com");
messageHelper.setTo(recipient);
messageHelper.setSubject("Sample mail subject");
String content = mailContentBuilder.build(message);
messageHelper.setText(content, true);
};
try {
if (looger.isDebugEnabled()) {
looger.debug("sending email to " + recipient);
}
mailSender.send(messagePreparator);
} catch (MailException e) {
looger.error(e.getMessage());
}
}
}
I want to create a ServiceConfig for testing purposes but I don't know how to instantiate the class MailClient because has no default constructor and the constructor MailClient() is undefined
#Configuration
public class ServiceConfig {
#Bean
public SmsService smsService() {
return new AWSSMSSender();
}
#Bean
public MailClient mailClient() {
return new MailClient();
}
}
Using the solution proposed:
return new MailClient(null, null) {
#Override
public void prepareAndSend(String recipient, String message)
{
// do nothing
}
};
I got this error:
No qualifying bean of type 'org.springframework.mail.javamail.JavaMailSender' available: expected at least 1 bean which qualifies as autowire candidate.
Dependency annotations: {#org.springframework.beans.factory.annotation.Autowired(required=true)}

Answer 1

You can user GreenMail for testing your email functionality in Spring Boot
You can refer this link : http://dolszewski.com/spring/sending-html-mail-with-spring-boot-and-thymeleaf/

Answer 2

It depends on what you want to do, send the email in tests (maybe with a test smpt server) or just simulate sending. In the second case you could subclass MailClient to do nothing in prepareAndSend and then use an instance of it.
return new MailClient(null, null) {
#Override
public void prepareAndSend(String recipient, String message)
{
// do nothing
}
};

Answer 3

You should use Stubbing.
The stubbing approach is easy to use and involves no extra dependencies for the unit test. The basic technique is to implement the collaborators as concrete classes which only exhibit the small part of the overall behaviour of the collaborator which is needed by the class under test. As an example consider the case where a service implementation is under test.