This project shows how to unit test some Java code sending e-mail. If you want a quick overview, just take a look at the simple test class src/test/../BirthdayCelebrationTest.java

For more details read through.

The test code uses Wiser as an SMTP in memory server. Add this dependency to your project :

testCompile 'org.subethamail:subethasmtp:3.1.7'  

In the test setup, you can now instantiate the SMTP server :

Wiser inMemorySmtpServer = new Wiser();

You can then read the emails send during the tests :

inMemorySmtpServer.getMessages()

And write some assertions (this example uses AssertJ):

assertThat(inMemorySmtpServer.getMessages())
        .extracting("envelopeSender", "envelopeReceiver", "mimeMessage.content")
        .containsOnly(
                tuple("[email protected]", "[email protected]", "Bonjour, pour tes 28 ans l'équipe te souhaite un très bon anniversaire !" + System.lineSeparator()),
                tuple("[email protected]", "[email protected]", "Bonjour, pour tes 28 ans l'équipe te souhaite un très bon anniversaire !" + System.lineSeparator())
        );

Don't forget to cleanup the server between tests :

@After
public void afterTest(){
    inMemorySmtpServer.stop();
}