Unit Testing (JUnit 5 & Mockito)

Isolated Unit Testing

Unit tests verify isolated class logic without starting a slow Spring IoC container.

Production Code Example:

package com.anujsingh.digitalguru;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.*;
import org.mockito.junit.jupiter.MockitoExtension;
import static org.mockito.Mockito.*;

@ExtendWith(MockitoExtension.class)
class ServiceTest {
    @Mock private PaymentRepository repo;
    @InjectMocks private PaymentService service;

    @Test void testPay() {
        service.pay();
        verify(repo, times(1)).save();
    }
}

Key Architectural Concepts & Best Practices:

When working with Unit Testing (JUnit 5 & Mockito) in enterprise Spring Boot applications, keep these key architectural guidelines in mind:

• Separation of Concerns: Maintain a strict boundary between HTTP endpoints, service logic, and database persistence layers.
• Framework Conventions: Rely on Spring Boot auto-configuration defaults whenever possible, overriding settings only via application.yml or @Configuration classes when customized behavior is required.
• Production Monitoring & Reliability: Ensure proper exception handling, thread-safety, and resource cleanup to prevent memory leaks and unexpected runtime downtime.
• Developer Ergonomics: Write clean, self-documenting code with modern Java features (Records, Lambdas, Streams) to simplify code reviews and maintenance.

Summary Takeaway:

Mastering Unit Testing (JUnit 5 & Mockito) ensures that your Java & Spring Boot backend microservices remain maintainable, secure, and compliant with modern enterprise software engineering standards.