assertThrows usage in JUnit - Test Execution Trace

Test Overview

This test checks that a method throws the expected exception when given invalid input. It verifies that assertThrows correctly catches the exception type.

Test Code - JUnit

JUnit

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

class Calculator {
    int divide(int a, int b) {
        return a / b;
    }
}

public class CalculatorTest {
    @Test
    void testDivideByZeroThrows() {
        Calculator calc = new Calculator();
        assertThrows(ArithmeticException.class, () -> calc.divide(10, 0));
    }
}

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test starts	JUnit test runner initialized	-	PASS
2	CalculatorTest.testDivideByZeroThrows method invoked	Calculator instance created	-	PASS
3	assertThrows called with ArithmeticException.class and lambda dividing 10 by 0	Lambda executed, division by zero attempted	Check if ArithmeticException is thrown	PASS
4	ArithmeticException thrown by divide method	Exception caught by assertThrows	Exception type matches expected ArithmeticException	PASS
5	Test completes successfully	Test runner reports test passed	assertThrows assertion passed	PASS

Failure Scenario

Failing Condition: divide method does not throw ArithmeticException when dividing by zero

Execution Trace Quiz - 3 Questions

What does assertThrows verify in this test?

A That the divide method throws ArithmeticException when dividing by zero

B That the divide method returns zero when dividing by zero

C That no exception is thrown during division

D That the divide method throws NullPointerException

Key Result

Use assertThrows to clearly and safely verify that a specific exception is thrown by a code block, improving test clarity and correctness.