Test independence in JUnit - Build an Automation Script

Verify that each test runs independently without relying on others

Preconditions (2)

Step 1: Create a test class CalculatorTest

Step 2: Write a test method testAddition that verifies add(2, 3) returns 5

Step 3: Write a test method testSubtraction that verifies subtract(5, 3) returns 2

Step 4: Run tests individually and together

Step 5: Verify that each test passes regardless of the order or if run alone

✅ Expected Result: Both testAddition and testSubtraction pass independently without any dependency on each other

Automation Requirements - JUnit 5

Assertions Needed:

assertEquals for verifying expected and actual results

Best Practices:

Each test method should be independent and not rely on shared state

Use @BeforeEach to set up fresh objects if needed

Avoid static or shared mutable state between tests

Automated Solution

JUnit

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

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

    int subtract(int a, int b) {
        return a - b;
    }
}

public class CalculatorTest {
    private Calculator calculator;

    @BeforeEach
    void setUp() {
        calculator = new Calculator();
    }

    @Test
    void testAddition() {
        int result = calculator.add(2, 3);
        assertEquals(5, result, "2 + 3 should equal 5");
    }

    @Test
    void testSubtraction() {
        int result = calculator.subtract(5, 3);
        assertEquals(2, result, "5 - 3 should equal 2");
    }
}

This test class CalculatorTest uses JUnit 5 to verify the Calculator methods.

The @BeforeEach method setUp() creates a new Calculator instance before each test. This ensures no shared state between tests.

Each test method (testAddition and testSubtraction) runs independently and asserts expected results using assertEquals.

Running tests individually or together will pass because they do not depend on each other.

Common Mistakes - 3 Pitfalls

Sharing the same Calculator instance across tests without resetting

Writing tests that depend on the order of execution

Using static variables to store test data or results

Bonus Challenge

Now add a test for multiplication with three different input pairs using parameterized tests

Show Hint