Dummy objects in JUnit - Build an Automation Script

Use dummy objects to satisfy method parameters in unit test

Preconditions (2)

Step 1: Create a dummy object to pass as a parameter to a method that requires an object but does not use it

Step 2: Write a unit test for Calculator.add method that requires a dummy object parameter

Step 3: Call the add method with two integers and the dummy object

Step 4: Verify the add method returns the correct sum

✅ Expected Result: The test passes successfully, confirming the add method works and the dummy object satisfies the parameter requirement without affecting the test

Automation Requirements - JUnit 5

Assertions Needed:

Assert that the add method returns the correct sum

Best Practices:

Use dummy objects only to fill parameters not used in the test

Keep dummy objects simple and minimal

Use @Test annotation for test methods

Use assertions from org.junit.jupiter.api.Assertions

Automated Solution

JUnit

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

class Calculator {
    // Method that requires a dummy object parameter but does not use it
    public int add(int a, int b, Object dummy) {
        return a + b;
    }
}

public class CalculatorTest {

    // Dummy object class
    static class DummyObject {}

    @Test
    void testAddWithDummyObject() {
        Calculator calculator = new Calculator();
        DummyObject dummy = new DummyObject(); // dummy object to satisfy parameter

        int result = calculator.add(5, 7, dummy);

        assertEquals(12, result, "The add method should return the sum of two numbers");
    }
}

This test shows how to use a dummy object to satisfy a method parameter that is not used in the logic. The Calculator.add method requires three parameters, but the third parameter is not used. We create a simple DummyObject class and pass an instance to the method. The test asserts that the sum is correct, ignoring the dummy object. This keeps the test focused and simple.

Common Mistakes - 3 Pitfalls

Using a real object with complex behavior instead of a simple dummy

Not using @Test annotation on the test method

Asserting on the dummy object instead of the actual method result

Bonus Challenge

Now add data-driven testing with 3 different pairs of integers to test the add method with dummy objects

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