[Java] Test Java mail by GreenMail

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要如何對JavaMail-API做單元測試呢? 在Stack Overflow上不少人推薦 GreenMail，GreenMail支援SMTP, POP3, IMAP，可以對sender和receiver進行測試，就來試用看看。

Sender

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public class MailSenderTest {

    private GreenMail greenMail;
    private MimeMessage message;

    @Before
    public void setUp() throws Exception {
        greenMail = new GreenMail(ServerSetupTest.SMTP);
        greenMail.start();

        Properties properties = System.getProperties();
        properties.put("mail.smtp.host", "localhost");
        properties.put("mail.smtp.port", ServerSetupTest.SMTP.getPort());
        Session session = Session.getInstance(properties);
        message = new MimeMessage(session);
        message.setFrom(new InternetAddress("test@test.com"));
        message.setRecipients(Message.RecipientType.TO,
                InternetAddress.parse("test1@test.com", false));
        message.setSubject("subject");
        message.setText("text");
        message.setSentDate(new Date());
    }

    @After
    public void tearDown() throws Exception {
        greenMail.stop();
    }

    @Test
    public void testSend() throws Exception {
        // [Start] Replace this with your send code        
        // Sender.send(message);
        // [End]
        
        MimeMessage[] messages = greenMail.getReceivedMessages();
        Assert.assertNotNull(messages);
        Assert.assertEquals(1, messages.length);
        MimeMessage m = messages[0];
        Assert.assertEquals("subject", m.getSubject());
        Assert.assertTrue(String.valueOf(m.getContent()).contains("text"));
        Assert.assertEquals("test@test.com", m.getFrom()[0].toString());
    }
}

Receiver

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public class MailReceiverTest {

    private GreenMail greenMail;
    private String subject;
    private String body;

    @Before
    public void setUp() throws Exception {
        greenMail = new GreenMail(ServerSetupTest.SMTP);
        greenMail.start();

        subject = GreenMailUtil.random();
		body = GreenMailUtil.random();
		GreenMailUtil.sendTextEmailTest("test@localhost.com", "test1@localhost.com", subject, body);
    }

    @After
    public void tearDown() throws Exception {
        greenMail.stop();
    }

    @Test
    public void testReceiver() throws Exception {
        // [Start] Replace this with your receive code
        // Message message = Receiver.receive();
        // [End]
        
		Assert.assertNotNull(message);
		Assert.assertEquals(message.getTo(), "test@localhost.com");
		Assert.assertEquals(message.getFrom(), "test1@localhost.com");
		Assert.assertEquals(message.getSubject(), subject);
		Assert.assertEquals(message.getBody(), body);
    }
}

使用GreenMail進行測試，嚴格來說並不屬於unit test，某種程度來說它也是屬於mail server，否則就必須mock Transport和Session。是否能透過mock Transport和Session來達到測試效果，這跟你的mail class設計有關。以實用性、方便性和功能性，GreenMail算是一個不錯測試mail的framework。

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