Unit Testing with JUnit

Unit testing is the practice of testing small units of code (typically methods) in isolation to ensure they work correctly. JUnit is the most popular testing framework for Java.

Writing a Test Case

A test case is a method annotated with @Test.

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

public class CalculatorTest {

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

Common Annotations

• @Test: Identifies a method as a test method.
• @BeforeEach: Executed before each test method.
• @AfterEach: Executed after each test method.
• @BeforeAll: Executed once before all test methods in the class.
• @AfterAll: Executed once after all test methods in the class.

Common Assertions

• assertEquals(expected, actual)
• assertTrue(condition)
• assertFalse(condition)
• assertNull(object)
• assertNotNull(object)
• assertThrows(Exception.class, () -> { ... })

Exception Testing

@Test
void testException() {
    assertThrows(ArithmeticException.class, () -> {
        int result = 10 / 0;
    });
}