Spring Mail Integration Testing with JUnit and GreenMail Example

By：Roy.LiuLast updated：2019-08-10

In this example we show how to use Spring Mail and write Integration Tests using JUnit and GreenMail. We start by writing a simple email service that sends out emails. We want to verify that this email service sends out correct emails, so we use GreenMail – which is an open source test suite of email servers for testing purposes.

Project Structure

Let’s start by looking at our project structure.

Maven Dependencies

We use Apache Maven to manage our project dependencies. Make sure the following dependencies reside on your class-path.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
                             http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>
    <groupId>com.memorynotfound.mail</groupId>
    <artifactId>mail-integration-test</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <url>https://memorynotfound.com</url>
    <name>Spring MAIL - ${project.artifactId}</name>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.7.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-mail</artifactId>
        </dependency>

        <!-- testing -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.icegreen</groupId>
            <artifactId>greenmail</artifactId>
            <version>1.5.5</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

Mail Object

We are using this Mail object to pass as an argument for our EmailService to encapsulate the details of an email message and content.

package com.memorynotfound.mail;

public class Mail {

    private String from;
    private String to;
    private String subject;
    private String content;

    public Mail() {
    }

    public Mail(String from, String to, String subject, String content) {
        this.from = from;
        this.to = to;
        this.subject = subject;
        this.content = content;
    }

    public String getFrom() {
        return from;
    }

    public void setFrom(String from) {
        this.from = from;
    }

    public String getTo() {
        return to;
    }

    public void setTo(String to) {
        this.to = to;
    }

    public String getSubject() {
        return subject;
    }

    public void setSubject(String subject) {
        this.subject = subject;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    @Override
    public String toString() {
        return "Mail{" +
                "from='" + from + '\'' +
                ", to='" + to + '\'' +
                ", subject='" + subject + '\'' +
                ", content='" + content + '\'' +
                '}';
    }
}

Sending Email Service

We use this service to demonstrate how to send a simple email, which we can verify in our integration tests.

package com.memorynotfound.mail;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.mail.SimpleMailMessage;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.stereotype.Service;

@Service
public class EmailService {

    @Autowired
    private JavaMailSender emailSender;

    public void sendSimpleMessage(Mail mail){
        SimpleMailMessage message = new SimpleMailMessage();
        message.setSubject(mail.getSubject());
        message.setText(mail.getContent());
        message.setTo(mail.getTo());
        message.setFrom(mail.getFrom());

        emailSender.send(message);
    }

}

Bootstrap Application

We use spring boot to bootstrap our application.

package com.memorynotfound.mail;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {

    public static void main(String[] args) throws Exception {
        SpringApplication.run(Application.class, args);
    }

}

Test Email Configuration Properties

We configure integration tests using the application-test.yml file which is located in the src/test/resources folder.

# application.yml

spring:
  mail:
    default-encoding: UTF-8
    host: localhost
    jndi-name:
    username: username
    password: secret
    port: 2525
    properties:
      mail:
        debug: false
        smtp:
          debug: false
          auth: true
          starttls: true
    protocol: smtp
    test-connection: false

Create SmtpServerRule

We create a custom JUnit Rule called SmtpServerRule by extending from the ExternalResource class. In this class we start and stop a GreenMail server before and after each Integration Test. This allows us to intercept incoming emails.

package com.memorynotfound.mail.test;

import com.icegreen.greenmail.util.GreenMail;
import com.icegreen.greenmail.util.ServerSetup;
import org.junit.rules.ExternalResource;
import javax.mail.internet.MimeMessage;

public class SmtpServerRule extends ExternalResource {

    private GreenMail smtpServer;
    private int port;

    public SmtpServerRule(int port) {
        this.port = port;
    }

    @Override
    protected void before() throws Throwable {
        super.before();
        smtpServer = new GreenMail(new ServerSetup(port, null, "smtp"));
        smtpServer.start();
    }

    public MimeMessage[] getMessages() {
        return smtpServer.getReceivedMessages();
    }

    @Override
    protected void after() {
        super.after();
        smtpServer.stop();
    }
}