Why exception testing validates error handling in JUnit - Test Execution Impact

Test Overview

This test checks that the method correctly throws an exception when given invalid input. It verifies that the error handling works as expected by catching the exception.

Test Code - JUnit 5

JUnit

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class CalculatorTest {

    @Test
    void testDivideByZeroThrowsException() {
        Calculator calc = new Calculator();
        Exception exception = assertThrows(ArithmeticException.class, () -> {
            calc.divide(10, 0);
        });
        assertEquals("Division by zero", exception.getMessage());
    }
}

class Calculator {
    public int divide(int a, int b) {
        if (b == 0) {
            throw new ArithmeticException("Division by zero");
        }
        return a / b;
    }
}

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test starts	JUnit test runner initialized	-	PASS
2	Calculator object created	Calculator instance ready	-	PASS
3	Calls divide(10, 0)	Method executes and throws ArithmeticException	assertThrows verifies ArithmeticException is thrown	PASS
4	Checks exception message equals 'Division by zero'	Exception caught with message 'Division by zero'	assertEquals verifies exception message	PASS
5	Test ends	Test passed successfully	-	PASS

Failure Scenario

Failing Condition: Method does not throw ArithmeticException when dividing by zero

Execution Trace Quiz - 3 Questions

What does the test verify about the divide method?

A It throws ArithmeticException when dividing by zero

B It returns zero when dividing by zero

C It throws NullPointerException when dividing by zero

D It returns the correct division result

Key Result

Exception testing ensures that error handling code runs correctly by verifying that the expected exceptions are thrown for invalid inputs.