Test Driven Development using JUnit5 and Mockito

Test Driven Development (TDD) is a software development approach where tests are written before the actual code implementation. Using JUnit 5 and Mockito, developers can create reliable and maintainable applications by validating behavior early. This approach improves code quality, reduces bugs, and ensures better design through continuous testing.

• Promotes writing tests first, followed by minimal code to pass those tests.
• Uses Mockito to mock dependencies and isolate units for accurate testing.
• Encourages refactoring while maintaining correctness through automated tests.

Step-by-Step Implementation of JUnit5 and Mockito

This section demonstrates how to set up a Maven-based Java project and systematically write unit tests using JUnit 5 along with Mockito to mock dependencies and verify application behavior effectively.

Step 1: Create a Maven Project

Create a Maven project using your IDE or command line.

• Ensure Java version is properly configured (Java 11 in your case).
• Use standard Maven directory structure.

Step 2: Add Required Dependencies (pom.xml)

Include dependencies for JUnit 5, assertions, and testing tools.

• JUnit Jupiter (API + Engine)
• AssertJ / Hamcrest for assertions
• Maven Surefire Plugin for running tests

pom.xml

Project Structure:

Step 3: Create Base Model Classe

Create basic POJO classes:

• BaseEntity
• Geek
• Author
• AuthorType (enum)

BaseEntity.java

Step 4: Create Domain Models

• Extends BaseEntity
• Contains firstName, lastName

Geek.java

Author.java

• Extends Geek
• Adds address, city, telephone

AuthorType.java

• Enum with values FREELANCING, COMPANY

Step 5: Create Controller Layer

• Handles user requests
• Uses AuthorService

AuthorController.java

Step 6: Create Repository Layer

Define repository interface:

AuthorRepository.java

Step 7: Create Service Layer

Define service interface and implementation.

AuthorService.java: Defines business methods

AuthorMapService.java: Implements service using in-memory storage

Step 8: Create Base Test Interfaces

ControllerTests.java: Runs once before all tests

ModelRepeatedTests.java: Supports repeated test execution

ModelTests.java:Runs before each test

Step 9: Write Model Test Cases

AuthorTest.java:

Here we can see that can include more than one annotations

• @DisplayName: Purpose of the test and categorization can be done easily
• @Parameterized Tests: They are built in and adopt the best features from JUnit4Parameterized and JUnitParams of Junit4

It helps to go with @ValueSource. @EmptySource and @NullSource represent a single parameter. On running the above code, we can able to get the below output

Step 10: Write Geek Test

GeekTest.java

• Uses grouped assertions
• Shows both success and failure cases

On running the above, the first test is ok and second one fails as expected and the actual one does not match

Step 11: Write Service Layer Tests

AuthorMapServiceTest.java

• @BeforeEach -> setup before every test
• @Nested -> group related tests
• @DisplayName -> readable test names

Step 12: Run Tests Using Maven

• Automatically detects test classes
• Executes using Surefire plugin

mvn test