Single assertion per test debate in JUnit - Test Execution Trace

Test Overview

This test checks if the calculator adds two numbers correctly. It uses a single assertion to verify the sum result.

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 testAddition() {
        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 - 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	add method called with 2 and 3	Method returns 5	-	PASS
4	assertEquals checks if result equals 5	Result is 5	Verify 5 == 5	PASS
5	Test ends	Test passed successfully	-	PASS

Failure Scenario

Failing Condition: Calculator add method returns incorrect sum

Execution Trace Quiz - 3 Questions

What does the single assertion in this test verify?

A That the Calculator object is created

B That the sum of 2 and 3 equals 5

C That the add method is called

D That the test runner starts

Key Result

Using a single assertion per test helps keep tests clear and easy to understand, making it simpler to find what went wrong when a test fails.