Unit testing concept in JUnit - Test Execution Trace

Test Overview

This test checks a simple method that adds two numbers. It verifies the method returns the correct sum.

Test Code - JUnit 5

JUnit

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

public class CalculatorTest {

    @Test
    public void testAdd() {
        Calculator calc = new Calculator();
        int result = calc.add(2, 3);
        assertEquals(5, result, "2 + 3 should equal 5");
    }
}

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

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test starts	JUnit test runner initialized	-	PASS
2	CalculatorTest class loaded	CalculatorTest and Calculator classes ready	-	PASS
3	testAdd method invoked	Calculator object created	-	PASS
4	add method called with arguments 2 and 3	Inside add method, inputs received	-	PASS
5	add method returns 5	Result 5 returned to testAdd	-	PASS
6	assertEquals checks if result equals 5	Comparing expected 5 and actual 5	assertEquals(5, result)	PASS
7	Test completes successfully	Test runner records pass	-	PASS

Failure Scenario

Failing Condition: add method returns incorrect sum

Execution Trace Quiz - 3 Questions

What does the testAdd method verify?

A That the Calculator class exists

B That adding 2 and 3 returns 5

C That the add method throws an exception

D That 2 plus 3 equals 6

Key Result

Unit tests should focus on small pieces of code, like one method, to check they work correctly in isolation.