Unit Testing with Spring Boot

What You’ll Learn 📚

• Core concepts of unit testing
• Setting up a Spring Boot project for testing
• Writing simple to complex unit tests
• Troubleshooting common issues

Introduction to Unit Testing

Unit testing is like a health check-up for your code. It ensures that each part of your application works as expected. In Spring Boot, unit testing is crucial because it helps you catch bugs early, making your code more reliable and maintainable.

Key Terminology

• Unit Test: A test that checks a small part of your application, usually a single function or method.
• JUnit: A popular testing framework for Java applications.
• Mocking: Creating fake objects that simulate the behavior of real objects in controlled ways.

Getting Started with a Simple Example

import static org.junit.jupiter.api.Assertions.assertEquals;import org.junit.jupiter.api.Test;public class CalculatorTest {    @Test    void testAddition() {        Calculator calculator = new Calculator();        int result = calculator.add(2, 3);        assertEquals(5, result, "2 + 3 should equal 5");    }}

Progressively Complex Examples

import static org.mockito.Mockito.*;import org.junit.jupiter.api.Test;import org.mockito.InjectMocks;import org.mockito.Mock;import org.mockito.junit.jupiter.MockitoExtension;import org.junit.jupiter.api.extension.ExtendWith;@ExtendWith(MockitoExtension.class)public class UserServiceTest {    @Mock    private UserRepository userRepository;    @InjectMocks    private UserService userService;    @Test    void testFindUserById() {        User mockUser = new User("John", "Doe");        when(userRepository.findById(1L)).thenReturn(Optional.of(mockUser));        User user = userService.findUserById(1L);        assertEquals("John", user.getFirstName());    }}

import static org.junit.jupiter.api.Assertions.assertThrows;import org.junit.jupiter.api.Test;public class CalculatorTest {    @Test    void testDivisionByZero() {        Calculator calculator = new Calculator();        assertThrows(ArithmeticException.class, () -> calculator.divide(10, 0), "Division by zero should throw an exception");    }}

Common Questions and Answers

1. What is the difference between unit testing and integration testing?

   Unit testing focuses on individual components, while integration testing checks how components work together.

2. Why use mocking in tests?

   Mocking allows you to isolate the unit of work by simulating dependencies, making tests more reliable and faster.

3. How do I run my tests?

   Use your IDE’s test runner or run mvn test in the command line.

4. What if my test fails?

   Check the error message, ensure your code logic is correct, and verify your test setup.

Troubleshooting Common Issues

Ensure your dependencies are correctly set up in your pom.xml or build.gradle.

If a test fails, try debugging it to step through the code and see where it goes wrong.

Practice Exercises

• Write a unit test for a method that calculates the factorial of a number.
• Create a mock test for a service that sends emails.

Don’t worry if this seems complex at first. With practice, you’ll become more comfortable with unit testing. Keep experimenting and learning! 🌟

Additional Resources

• JUnit 5 User Guide
• Spring Boot Testing Guide