Java Test Case: Exception Testing

Last update on May 23 2025 13:13:44 (UTC/GMT +8 hours)

2. Assert Exception Thrown on Invalid Input

Write a Java test case to verify that a specific exception is thrown when a method is called with invalid input.

Sample Solution:

Java Code:

// ExceptionTest.java
import org.junit.Test;
import org.junit.runner.JUnitCore;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;

import static org.junit.Assert.*;

public class ExceptionTest {

    // Example class with a method that throws a specific exception
    public class ExampleClass {
        public int divide(int a, int b) {
            if (b == 0) {
                throw new ArithmeticException("Cannot divide by zero");
            }
            return a / b;
        }
    }

    // JUnit test case to verify the specific exception
    @Test(expected = ArithmeticException.class)
    public void testDivideByZero() {
        // Arrange
        ExampleClass example = new ExampleClass();

        // Act
        int result = example.divide(10, 0);

        // Assert (Exception is expected, so nothing to assert)
    }

    // Main function to run JUnit tests
    public static void main(String[] args) {
        Result result = JUnitCore.runClasses(ExceptionTest.class);

        // Check if there are any failures
        if (result.getFailureCount() > 0) {
            System.out.println("Test failed:");

            // Print details of failures
            for (Failure failure : result.getFailures()) {
                System.out.println(failure.toString());
            }
        } else {
            System.out.println("All tests passed successfully.");
        }
    }
}

Sample Output:

All tests passed successfully.

Explanation:

In the exercise above,

The "ExampleClass" has a "divide()" method that throws an "ArithmeticException" if the divisor is zero.
The "testDivideByZero" JUnit test case uses the @Test annotation with the expected attribute to specify that an "ArithmeticException" is expected to be thrown during the execution of the test.
The main() function uses JUnitCore.runClasses(ExceptionTest.class) to run the tests. If any test case fails, it prints details about the failure; otherwise, it prints a success message.

Flowchart:

For more Practice: Solve these Related Problems:

Write a Java program to create a test case that verifies a NullPointerException is thrown when a method receives a null argument.
Write a Java program to implement a test case that checks for an IllegalArgumentException when input parameters are out of bounds.
Write a Java program to create a test case that asserts a custom exception is thrown for invalid business logic inputs.
Write a Java program to design a test case that confirms a division by zero operation throws an ArithmeticException.

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