Unit Testing in Spring Boot Project using Mockito and Junit

20 June 2025

2

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 avoiding heavy configuration of XML which is present in spring
It provides easy maintenance and creation of REST endpoints
It includes embedded Tomcat-server
Deployment is very easy, 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 that can be 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. And 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
    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.

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> {
    @Query(
        "SELECT CASE WHEN COUNT(s) > 0 THEN TRUE ELSE FALSE END FROM Person s WHERE s.personId = ?1")
    Boolean
    isPersonExitsById(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 {
 
    @Autowired private PersonRepo repo;
 
    public List<Person> getAllPerson()
    {
        return this.repo.findAll();
    }
 
    public PersonService(PersonRepo repo)
    {
        // this keyword refers to current instance
        this.repo = repo;
    }
}

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;
 
@RestController
public class PersonController {
 
    @Autowired
    private PersonService personService;
 
    @GetMapping("/persons")
    public ResponseEntity<?> getAllPersons() {
        return ResponseEntity.ok(this.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 create one class named as PersonRepoTest.

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
    private Integer personId;
    private String personName;
    private String personCity;
}

Step 11: Unit Testing of Service Class

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

Java

// Java Program to Illustrate Unit Testing of Service Class
 
package com.demo.services;
 
import static org.mockito.Mockito.verify;
 
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;
 
    private PersonService personService;
 
    @BeforeEach void setUp()
    {
        this.personService
            = new PersonService(this.personRepo);
    }
 
    @Test void getAllPerson()
    {
        personService.getAllPerson();
        verify(personRepo).findAll();
    }
}

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

Unit Testing in Spring Boot Project using Mockito and Junit

Step by Step Implementation

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