**Course Title:** Comprehensive Java Programming: From Basics to Advanced Concepts **Section Title:** Testing and Debugging Java Applications **Topic:** Write unit tests for a Java project using JUnit and practice debugging using breakpoints and log statements.(Lab topic) **Overview** Unit testing is a crucial part of software development that ensures individual components of a program work correctly. JUnit is a popular testing framework for Java that provides a robust way to write and run unit tests. In this topic, we'll learn how to write unit tests for a Java project using JUnit and practice debugging using breakpoints and log statements. **Writing Unit Tests with JUnit** To write unit tests with JUnit, you need to create a test class that extends the `junit.framework.TestCase` class. The test class should contain methods that start with the word "test" followed by the name of the method being tested. These methods should be annotated with the `@Test` annotation to indicate that they are test methods. Here's an example of a simple test class: ```java import org.junit.Test; import static org.junit.Assert.assertEquals; public class CalculatorTest { @Test public void testAdd() { Calculator calculator = new Calculator(); int result = calculator.add(2, 2); assertEquals(4, result); } } ``` In this example, we're testing the `add` method of the `Calculator` class. The `assertEquals` method is used to verify that the result is equal to 4. **ASSERTION METHODS** JUnit provides a range of assertion methods that can be used to verify the result of a test. Here are some of the most common assertion methods: * `assertEquals(a, b)`: Verifies that `a` equals `b` * `assertNotEquals(a, b)`: Verifies that `a` does not equal `b` * `assertTrue(a)`: Verifies that `a` is true * `assertFalse(a)`: Verifies that `a` is false * `assertNull(a)`: Verifies that `a` is null * `assertNotNull(a)`: Verifies that `a` is not null **USING BEFORE AND AFTER METHODS** JUnit provides two methods that can be used to execute code before and after each test method: * `@Before`: This method is executed before each test method. It's typically used to initialize objects or set up test data. * `@After`: This method is executed after each test method. It's typically used to release resources or clean up test data. Here's an example: ```java import org.junit.Before; import org.junit.Test; import org.junit.After; public class CalculatorTest { private Calculator calculator; @Before public void setup() { calculator = new Calculator(); } @Test public void testAdd() { int result = calculator.add(2, 2); assertEquals(4, result); } @After public void cleanup() { calculator = null; } } ``` **DEBUGGING WITH BREAKPOINTS AND LOG STATEMENTS** Breakpoints and log statements are essential tools for debugging Java programs. A breakpoint is a location in your code where the debugger will pause execution, allowing you to examine the current state of your program. Log statements are used to print output to the console, providing valuable information about the execution of your program. **Setting Breakpoints in Eclipse** To set a breakpoint in Eclipse, follow these steps: 1. Open your Java program in the Eclipse editor 2. Click on the line of code where you want to set the breakpoint 3. Right-click on the line and select **Toggle Breakpoint** To debug your program, follow these steps: 1. Click on the **Debug** button or press F11 2. Eclipse will launch the debugger and execute your program until it reaches the breakpoint 3. You can then examine the current state of your program, including variable values and the call stack **Using Log Statements** Log statements are used to print output to the console. You can use the `System.out.println()` method to print output. Here's an example: ```java public class Calculator { public int add(int a, int b) { System.out.println("Adding " + a + " and " + b); return a + b; } } ``` **Practical Lab Exercise** For this lab exercise, you will create a Java program that simulates a Bank Account. The program should have methods to deposit, withdraw, and check the balance. You will write unit tests for each method using JUnit. 1. Create a new Java project in Eclipse 2. Create a class called `BankAccount` with methods for deposit, withdrawal, and checking the balance 3. Create a test class called `BankAccountTest` with unit tests for each method 4. Use breakpoints and log statements to debug your program **Additional Resources** For more information on JUnit, see the official JUnit documentation: <https://junit.org/junit5/docs/current/user-guide/> **Try It Yourself** Complete the lab exercise and practice writing unit tests with JUnit. If you have any questions or need help, please feel free to ask. In our next topic, we'll be discussing Introduction to build tools: Maven and Gradle.