Unit Testing in Spring Boot Project using Mockito and Junit

Spring Boot is built on the top of the spring and contains all the features of spring. And is becoming a favorite of developers these days because of its rapid production-ready environment which enables the developers to directly focus on the logic instead of struggling with the configuration and setup. Spring Boot is a microservice-based framework and making a production-ready application in it takes very little time. Following are some of the features of Spring Boot:

• It allows for avoiding heavy configuration of XML which is present in spring.
• It provides easy maintenance and creation of REST endpoints.
• It includes an embedded Tomcat server.
• Deployment is straightforward, war and jar files can be easily deployed in the Tomcat server.

Mockito is an open-source testing framework used for unit testing of Java applications. It plays a vital role in developing testable applications. Mockito is used to mock interfaces so that a dummy functionality can be added to a mock interface used in Unit Testing. Unit Testing is a type of software testing in which individual components of the software are tested. The major objective of using the Mockito framework is to simplify the development of a test by mocking external dependencies and using them in the test code. As a result, Mockito provides a simpler test code that is easier to understand, more readable, and modifiable. Mockito can also be used with other testing frameworks like JUnit and TestNG. JUnit framework is a Java framework that is also used for testing. Now, JUnit is used as a standard when there is a need to perform testing in Java. So, in this article, we are going to perform Unit Testing in Spring Boot Project using Mockito and JUnit.

Step-by-Step Implementation

Step 1: Refer to this article How to Create a Spring Boot Project with IntelliJ IDEA and create a Spring Boot project. 

Step 2: Add the following dependency as listed below as follows:

• Spring Web
• MySQL Database
• Lombok
• Spring Data JPA

Example: pom.xml File

XML

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.demo</groupId>
    <artifactId>BootDemoApp</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>BootDemoApp</name>
    <description>BootDemoApp</description>
    <properties>
        <java.version>16</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>


    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

Step 3: Create the packages and files as seen in the below image. Below is the complete file structure of this project.

Note:

• Green Rounded Icon ‘I’ Buttons are Interface.
• Blue Rounded Icon ‘C’ Buttons are Classes.

Step 4: Inside the entity package

It is done via creating a simple POJO class inside the Person.java file.

Java

package com.demo.entities;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
// Class
public class Person {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer personId;
    private String personName;
    private String personCity;
}

Step 5: Inside the repository package

Create a simple interface and name the interface as PersonRepo. This interface is going to extend the JpaRepository.

JpaRepository: It takes two generic Parameters. First of entity and other of Type of Primary Key. Here entity is Person and Integer is Primary Key.

Java

package com.demo.repo;

import com.demo.entities.Person;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;

// Interface
// Extends JpaRepository
public interface PersonRepo
    extends JpaRepository<Person, Integer> {
  //Spring data jpa  will automatically provide implementation for it when using existsBy{fieldName}
    Boolean existsById(Integer id);
}

Step 6: Inside the service package

Inside the package create one class named as PersonService. 

Java

package com.demo.services;

import com.demo.entities.Person;
import com.demo.repo.PersonRepo;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

// Annotation
@Service

// Class
public class PersonService {
  //No need to use @Autowired when using Constructor Injection
  //Dependencies are final

   private final PersonRepo repo;
   public PersonService(PersonRepo repo)
    {
        // this keyword refers to current instance
        this.repo = repo;
    }

    public List<Person> getAllPerson()
    {
        return repo.findAll();
    }


}

Step 7: Inside the controller package

Inside the package create one class named as PersonController.

Java

package com.demo.controllers;

import com.demo.services.PersonService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import com.demo.entity.Person
@RestController
public class PersonController {
  //Constructor Based Injection No need of using @Autowired
  private final PersonService personService;
  public PersonController(PersonService personService){
  this.personService=personService;
}

    @GetMapping("/persons")
    public ResponseEntity<List<Person>> getAllPersons() {
        return ResponseEntity.ok(personService.getAllPerson());
    }
}

Step 8: Below is the code for the application.properties file

server.port=8082
# Configuration for MySQL Database
spring.jpa.hibernate.ddl-auto=update
spring.datasource.url=jdbc:mysql://localhost:3306/schooldb
spring.datasource.username=amiya559
spring.datasource.password=password.123
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.jpa.show-sql:true

Now your sample spring boot project is ready, and we are going to perform unit testing in this sample project. 

Step 9: Create the following packages and the classes as shown in the below image. (Inside the green color box)

Step 10: Unit Testing of Repository Class

Inside the test > repo package creates one class named as PersonRepoTest. 

Java

package com.demo.entities;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.Builder;
import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
// Class
public class Person {
    @Id
    private Integer personId;
    private String personName;
    private String personCity;
}

Step 11: Unit Testing of Service Class

Inside the test > services package creates one class named as PersonServiceTest. 

Java

// Java Program to Illustrate Unit Testing of Service Class

package com.demo.services;
//USing BDD Mockito
import static org.mockito.BDDMockito.verify;
import static org.mockito.BDDMockito.given;
import static org.assertj.core.api.Assertions.assertThat;

import com.demo.repo.PersonRepo;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;

@ExtendWith(MockitoExtension.class)

// Main class
class PersonServiceTest {

    @Mock
  private PersonRepo personRepo;
  //When using Mockito Use @InjectMocks to inject
  //Mocked beans to following class
    @InjectMocks
  private PersonService personService;

    @Test
  void getAllPerson()
    {
      //given
       Person person= new Person( 1,"Ahnis","Gotham");
       Person person2= new Person(2,"Saksham","New york");
      //When
       given(personRepo.findAll())
      .willReturn(List.of(person,person2));
      var  personList = personService.getAllPerson();
       //Then
    //Make sure to import assertThat From org.assertj.core.api package
         assertThat(personList).isNotNull();
         assertThat(personList.size()).isEqualTo(2);
  }
}

Similarly, we can perform testing of different units of your spring boot project.