Why assertions verify expected outcomes in JUnit - Test Execution Impact

Test Overview

This test checks if the addition method returns the correct sum. It verifies the expected outcome using assertions to ensure the method works as intended.

Test Code - JUnit

JUnit

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

public class CalculatorTest {

    public int add(int a, int b) {
        return a + b;
    }

    @Test
    public void testAdd() {
        CalculatorTest calculator = new CalculatorTest();
        int result = calculator.add(2, 3);
        assertEquals(5, result, "Addition result should be 5");
    }
}

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test starts	JUnit test runner initialized	-	PASS
2	Creates CalculatorTest instance	CalculatorTest object ready	-	PASS
3	Calls add(2, 3) method	Method executes and returns 5	-	PASS
4	Assert that result equals 5	Result is 5	assertEquals(5, result)	PASS
5	Test ends successfully	Test passed with no errors	-	PASS

Failure Scenario

Failing Condition: The add method returns a wrong sum, e.g., 4 instead of 5

Execution Trace Quiz - 3 Questions

What does the assertion in the test verify?

A That the add method throws an exception

B That the add method returns the expected sum

C That the add method returns null

D That the add method runs without errors

Key Result

Assertions are essential because they confirm that the code behaves as expected, catching errors early by comparing actual results to expected outcomes.