assertSame and assertNotSame in JUnit - Test Execution Trace

Test Overview

This test checks if two object references point to the exact same object using assertSame, and verifies that two references do not point to the same object using assertNotSame.

Test Code - JUnit 5

JUnit

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

public class ReferenceTest {

    @Test
    void testAssertSameAndNotSame() {
        String a = "hello";
        String b = a;
        String c = new String("hello");

        // assertSame passes because a and b refer to the same object
        assertSame(a, b, "a and b should be the same object");

        // assertNotSame passes because a and c are different objects
        assertNotSame(a, c, "a and c should not be the same object");
    }
}

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test starts	JUnit test runner initialized	-	PASS
2	Assign String 'hello' to variable a	Variable a references String object "hello"	-	PASS
3	Assign variable b to reference the same object as a	Variable b references the same String object as a	-	PASS
4	Create new String object with value 'hello' and assign to c	Variable c references a new String object with value "hello"	-	PASS
5	assertSame(a, b) checks if a and b reference the same object	a and b reference the same String object	assertSame passes because references are identical	PASS
6	assertNotSame(a, c) checks if a and c reference different objects	a and c reference different String objects	assertNotSame passes because references are different	PASS
7	Test ends successfully	All assertions passed	-	PASS

Failure Scenario

Failing Condition: assertSame fails if the two references do not point to the same object, or assertNotSame fails if the two references point to the same object

Execution Trace Quiz - 3 Questions

What does assertSame verify in this test?

A That two variables have equal values

B That two variables point to the exact same object

C That two variables are not null

D That two variables are different objects

Key Result

Use assertSame to verify two variables point to the exact same object in memory, not just equal values. Use assertNotSame to confirm they are different objects. This helps catch subtle bugs related to object identity.