assertSame and assertNotSame in JUnit - Build an Automation Script

Verify assertSame and assertNotSame behavior in JUnit

Preconditions (2)

Step 1: Create two variables referencing the same object instance

Step 2: Use assertSame to verify both variables point to the same object

Step 3: Create two variables referencing different object instances with same content

Step 4: Use assertNotSame to verify these variables do not point to the same object

✅ Expected Result: assertSame passes when both variables reference the same object; assertNotSame passes when variables reference different objects

Automation Requirements - JUnit 5

Assertions Needed:

assertSame to check two references point to the same object

assertNotSame to check two references point to different objects

Best Practices:

Use descriptive variable names

Keep tests independent and focused

Use @Test annotation for test methods

Use meaningful assertion messages

Automated Solution

JUnit

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

public class AssertSameNotSameTest {

    @Test
    void testAssertSame() {
        String original = "JUnit";
        String reference = original;
        assertSame(original, reference, "Both references should point to the same object");
    }

    @Test
    void testAssertNotSame() {
        String first = new String("JUnit");
        String second = new String("JUnit");
        assertNotSame(first, second, "References should point to different objects even if content is same");
    }
}

The code imports JUnit 5 assertions and defines two test methods.

In testAssertSame, two variables point to the same String object. assertSame verifies they reference the exact same object.

In testAssertNotSame, two different String objects with the same content are created. assertNotSame verifies they are different objects in memory.

Each assertion includes a message to clarify the test intent if it fails.

Common Mistakes - 3 Pitfalls

Using assertEquals instead of assertSame to check object identity

Using assertSame on two different objects with same content

Not providing assertion messages

Bonus Challenge

Now add data-driven testing with 3 different object pairs to verify assertSame and assertNotSame

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