Junit/Mockito のみを使用し、送信前に MimeMessage がどのように形成されたかをテストすることが目標である場合は、以下の構成で十分です。
public class EmailServiceTest {
private EmailServiceImpl emailServiceImpl;
private JavaMailSender javaMailSender;
private MimeMessage mimeMessage;
@Before
public void before() {
mimeMessage = new MimeMessage((Session)null);
javaMailSender = mock(JavaMailSender.class);
when(javaMailSender.createMimeMessage()).thenReturn(mimeMessage);
emailServiceImpl = new EmailService(javaMailSender);
}
@Test
public void emailTest() {
String recipient = "example@example.com"
EmailRequest request = new EmailRequest();
request.setRecipient(recipient);
emailServiceImpl.send(request);
assertEquals(recipient, mimeMessage.getRecipients(RecipientType.TO)[0].toString());
}
}