Week 7 - Testing, Logging and Validation

📘 Overview

Welcome to Week 7 of the Learn Java for Beginners mentorship program.

Until now, we have focused on:

Core Java programming
Collections and exception handling
File IO and multithreading
Design patterns
Spring Boot development
JPA and Hibernate

In this week, we will focus on one of the most important aspects of backend engineering:

Writing reliable code
Validating user input
Logging application behavior
Testing backend applications

A backend application is not considered production-ready unless it is:

Properly tested
Easy to debug
Resilient against invalid input
Observable through logs

This week will help build those skills.

🎯 Learning Objectives

By the end of this week, the learner should be able to:

Understand the importance of automated testing
Write unit tests using JUnit 5
Understand assertions and test lifecycle
Test Spring Boot applications
Validate request payloads using Bean Validation
Handle validation failures gracefully
Implement application logging using SLF4J
Understand debugging and troubleshooting basics
Develop a testing mindset while writing code

📚 Topics Covered

1. Introduction to Testing

Why testing matters
Types of testing
Unit testing vs integration testing
Manual testing vs automated testing
Test-driven thinking

2. JUnit 5 Basics

Writing test classes
Using @Test
Assertions
Test lifecycle methods
Organizing test cases

3. Spring Boot Testing

Testing service classes
Testing REST controllers
Mocking dependencies
Introduction to Mockito

4. Validation

Bean Validation API
@Valid
@NotNull
@NotBlank
@Size
Handling validation exceptions

5. Logging

Why logging is important
Log levels
Using SLF4J
Structured logging practices
Logging errors and exceptions

6. Debugging and Troubleshooting

Reading stack traces
Common runtime issues
Using IntelliJ debugger
Breakpoints and step execution

🛠 Practical Activities

During this week, the learner will:

Write unit tests for service methods
Test REST API endpoints
Add validation annotations
Implement exception handling
Add application logging
Debug intentionally broken code
Review failed test scenarios

🧪 Tools and Technologies

The following tools and frameworks will be used:

Tool	Purpose
Java 17+	Backend Development
Spring Boot	REST API Development
JUnit 5	Unit Testing
Mockito	Mocking Framework
SLF4J	Logging
Maven	Build Management
IntelliJ IDEA	Development Environment
Postman	API Testing

📂 Week Structure

This week contains the following learning materials:

File	Purpose
study-material.md	Detailed concepts and explanations
exercises.md	Practice exercises
assignment.md	Weekly assignment
quiz.md	Concept validation
assessment.md	Weekly assessment criteria
review-checklist.md	Code review checklist
solutions.md	Reference solutions

🧠 Important Engineering Mindset

A good developer writes code that works.

A great backend engineer writes code that is:

Testable
Maintainable
Observable
Reliable
Debuggable

Testing is not a separate activity performed after development.

Testing is part of engineering.

📋 Expectations from the Learner

The learner is expected to:

Complete all exercises
Attempt quizzes honestly
Write clean and readable code
Practice debugging independently
Participate in weekly review discussions
Ask questions whenever concepts are unclear

🏁 End Goal of This Week