Why testing matters in Spring Boot - See It in Action

Why Testing Matters in Spring Boot

📖 Scenario: You are building a simple Spring Boot application that manages a list of books. To ensure your application works correctly and to avoid future bugs, you will add tests. Testing helps catch mistakes early and makes your code more reliable.

🎯 Goal: Build a Spring Boot project with a simple BookService class and write a test to check if the service returns the correct number of books.

📋 What You'll Learn

Create a BookService class with a method getBooks() that returns a list of book titles.

Add a configuration variable expectedBookCount to hold the expected number of books.

Write a test method in BookServiceTest that checks if getBooks() returns the expected number of books.

Use Spring Boot testing annotations to run the test.

💡 Why This Matters

🌍 Real World

Testing is essential in real projects to ensure your code works as expected and to prevent bugs from reaching users.

💼 Career

Knowing how to write and run tests in Spring Boot is a key skill for backend developers and improves code quality and maintainability.

1

Create the BookService class with a list of books

Create a class called BookService with a method getBooks() that returns a list containing exactly these three book titles: "Spring Basics", "Java Fundamentals", and "Testing Essentials".

Spring Boot

// Your code here

Hint

Use List.of() to create a fixed list of book titles.

2

Add expectedBookCount variable

Inside the BookService class, add a private integer variable called expectedBookCount and set it to 3.

Spring Boot

package com.example.demo.service;

import java.util.List;

public class BookService {
    // Add expectedBookCount variable here

    public List getBooks() {
        return List.of("Spring Basics", "Java Fundamentals", "Testing Essentials");
    }
}

Hint

Declare expectedBookCount as a private integer and assign it the value 3.

3

Write a test method to check book count

Create a test class called BookServiceTest in package com.example.demo.service. Inside it, write a test method called testGetBooksCount() that creates an instance of BookService and asserts that the size of the list returned by getBooks() equals expectedBookCount.

Spring Boot

// Your test class and method here

Hint

Use JUnit 5 @Test annotation and assertEquals to compare expected and actual values.

4

Add Spring Boot test annotation

In the BookServiceTest class, add the @SpringBootTest annotation above the class declaration to enable Spring Boot testing support.

Spring Boot

package com.example.demo.service;

import static org.junit.jupiter.api.Assertions.assertEquals;

import org.junit.jupiter.api.Test;

// Add @SpringBootTest annotation here
public class BookServiceTest {

    @Test
    public void testGetBooksCount() {
        BookService service = new BookService();
        assertEquals(service.expectedBookCount, service.getBooks().size());
    }
}

Hint

Import and add @SpringBootTest above the test class to enable Spring Boot context.

Practice

1. Why is testing important in a Spring Boot application?

easy

A. It makes the app run faster in production.

B. It helps catch bugs early and ensures the app works as expected.

C. It automatically fixes errors in the code.

D. It reduces the size of the application.

Solution

1. Step 1: Understand the purpose of testing

   Testing is done to find bugs early and verify that the application behaves correctly.

2. Step 2: Evaluate the options

   Only It helps catch bugs early and ensures the app works as expected. correctly states that testing helps catch bugs early and ensures expected behavior.

3. Final Answer:

   It helps catch bugs early and ensures the app works as expected. -> Option B

4. Quick Check:

   Testing importance = Catch bugs early [OK]

Hint: Testing finds bugs early and checks app behavior [OK]

Common Mistakes:

• Thinking testing makes app faster
• Believing testing fixes code automatically
• Confusing testing with app size optimization

2. Which annotation is used to write a test class in Spring Boot?

easy

A. @SpringBootTest

B. @Controller

C. @Service

D. @Repository

Solution

1. Step 1: Identify the test class annotation in Spring Boot

   @SpringBootTest is used to load the full application context for testing.

2. Step 2: Check other annotations

   @Controller, @Service, and @Repository are for app components, not tests.

3. Final Answer:

   @SpringBootTest -> Option A

4. Quick Check:

   Test class annotation = @SpringBootTest [OK]

Hint: Use @SpringBootTest to run Spring Boot tests [OK]

Common Mistakes:

• Using @Controller or @Service for tests
• Confusing component annotations with test annotations
• Forgetting to annotate test classes

3. What will happen when this Spring Boot test runs?

@SpringBootTest
public class MyAppTests {
  @Test
  void testSum() {
    int result = 2 + 3;
    assertEquals(5, result);
  }
}

medium

A. The test will pass because the sum is correct.

B. The test will be ignored automatically.

C. The test will cause a syntax error.

D. The test will fail because 2 + 3 is not 5.

Solution

1. Step 1: Analyze the test method

   The method calculates 2 + 3 and stores 5 in result, then checks if result equals 5.

2. Step 2: Determine test outcome

   Since 2 + 3 is 5, assertEquals(5, result) will pass without errors.

3. Final Answer:

   The test will pass because the sum is correct. -> Option A

4. Quick Check:

   2 + 3 = 5 test passes [OK]

Hint: Check if assertion matches calculation result [OK]

Common Mistakes:

• Thinking 2 + 3 is not 5
• Assuming syntax errors without checking code
• Believing tests run automatically without @Test

4. Identify the error in this Spring Boot test code:

@SpringBootTest
public class SampleTests {
  @Test
  void testMultiply() {
    int result = 3 * 4
    assertEquals(12, result);
  }
}

medium

A. The class should not be annotated with @SpringBootTest.

B. assertEquals is used incorrectly; it needs three arguments.

C. The @Test annotation is missing.

D. Missing semicolon after '3 * 4' causes a syntax error.

Solution

1. Step 1: Check syntax in the test method

   The line 'int result = 3 * 4' is missing a semicolon at the end, causing a syntax error.

2. Step 2: Verify other parts

   @Test annotation is present, assertEquals usage with two arguments is correct, and @SpringBootTest is valid for test class.

3. Final Answer:

   Missing semicolon after '3 * 4' causes a syntax error. -> Option D

4. Quick Check:

   Missing semicolon = syntax error [OK]

Hint: Look for missing semicolons in Java code [OK]

Common Mistakes:

• Ignoring missing semicolon errors
• Thinking assertEquals needs three arguments
• Assuming @Test annotation is missing

5. You want to test a Spring Boot service method that returns null sometimes. Which approach best ensures your test catches this case?

hard

A. Write a test that asserts the method never returns null.

B. Skip testing null cases to avoid test failures.

C. Write a test that checks for both null and valid return values.

D. Only test the method with valid inputs.

Solution

1. Step 1: Understand the method behavior

   The method can return null sometimes, so tests must handle both null and valid results.

2. Step 2: Choose the best testing approach

   Testing only valid inputs or skipping null cases misses bugs. Asserting never null is wrong if null is valid.

3. Final Answer:

   Write a test that checks for both null and valid return values. -> Option C

4. Quick Check:

   Test all cases including null = best practice [OK]

Hint: Test all possible return values including null [OK]

Common Mistakes:

• Ignoring null return cases in tests
• Assuming method never returns null
• Skipping tests for edge cases