Deterministic tests in JUnit - Test Execution Trace

Test Overview

This test checks that a simple calculator's addition method always returns the same result for the same inputs. It verifies the test is deterministic, meaning it produces consistent results every time it runs.

Test Code - JUnit 5

JUnit

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

public class CalculatorTest {

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

    @Test
    void testAdditionIsDeterministic() {
        Calculator calc = new Calculator();
        int result1 = calc.add(2, 3);
        int result2 = calc.add(2, 3);
        assertEquals(result1, result2, "Addition results should be the same for same inputs");
        assertEquals(5, result1, "2 + 3 should equal 5");
    }
}

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test starts	JUnit test runner initialized	-	PASS
2	Calculator object is created	Calculator instance ready	-	PASS
3	Call add(2, 3) first time	Method returns 5	-	PASS
4	Call add(2, 3) second time	Method returns 5 again	-	PASS
5	Assert result1 equals result2	Both results are 5	Check if 5 == 5	PASS
6	Assert result1 equals 5	Result1 is 5	Check if 5 == 5	PASS
7	Test ends successfully	Test passed with no errors	-	PASS

Failure Scenario

Failing Condition: The add method returns different results for the same inputs

Execution Trace Quiz - 3 Questions

What does the test verify about the add method?

A It always returns the same result for the same inputs

B It returns random results

C It throws an exception

D It modifies input values

Key Result

Deterministic tests always produce the same result for the same inputs, making debugging easier and tests reliable.