assertEquals in JUnit - Build an Automation Script

Verify addition method returns correct sum

Preconditions (1)

Step 1: Call add(2, 3) method

Step 2: Capture the returned result

Step 3: Compare the result with expected value 5

✅ Expected Result: The add method returns 5 when called with inputs 2 and 3

Automation Requirements - JUnit 5

Assertions Needed:

Verify that the actual sum equals the expected sum using assertEquals

Best Practices:

Use @Test annotation for test methods

Use descriptive method names

Keep tests independent and simple

Use assertEquals(expected, actual) with a message for clarity

Automated Solution

JUnit

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

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

public class CalculatorTest {

    @Test
    void testAddReturnsCorrectSum() {
        Calculator calculator = new Calculator();
        int result = calculator.add(2, 3);
        assertEquals(5, result, "Addition of 2 and 3 should be 5");
    }
}

This test class CalculatorTest uses JUnit 5 to check the add method of the Calculator class.

The @Test annotation marks the test method testAddReturnsCorrectSum. Inside, it creates a Calculator object, calls add(2, 3), and stores the result.

Then, assertEquals compares the expected value 5 with the actual result. If they match, the test passes; otherwise, it fails and shows the message.

This clear structure helps beginners understand how to write simple unit tests with assertions.

Common Mistakes - 3 Pitfalls

Swapping expected and actual parameters in assertEquals

{'mistake': 'Not using @Test annotation on test methods', 'why_bad': "Without @Test, the test method won't run automatically, so tests are skipped silently.", 'correct_approach': 'Always annotate test methods with @Test to ensure they run.'}

Not providing a failure message in assertEquals

Bonus Challenge

Now add data-driven testing with 3 different pairs of inputs and expected sums

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