Writing Test Cases with JUnit

JUnit is a widely-used testing framework for Java that allows developers to write repeatable tests for individual components of their applications. It’s integral to test-driven development (TDD) and continuous integration pipelines.

Why use JUnit:

• Encourages modular and testable code.
• Integrates with build tools (Maven, Gradle).
• Supports test automation and CI/CD.
• Helps catch bugs early in development.

Structure of a JUnit test:

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

public class CalculatorTest {

    @Test
    public void testAddition() {
        Calculator calc = new Calculator();
        assertEquals(5, calc.add(2, 3));
    }
}

Annotations:

• @Test: Marks a method as a test.
• @BeforeEach: Runs before each test method.
• @AfterEach: Runs after each test method.
• @BeforeAll / @AfterAll: Run once before/after all tests.

Best practices:

• Keep tests small and focused.
• Name test methods clearly (testUserLoginShouldReturnSuccess).
• Use mocks for external dependencies.
• Group related tests in test suites.

JUnit is essential for Java developers. Writing good test cases not only validates your code but also ensures long-term maintainability and stability in your applications.