Module 2: Unit Testing: Test Driven Development

Learning Objectives

• Understand the principles of test driven development (TDD)
• Understand the advantages and potential disadvantages to enforcing a TDD approach
• Learn the red-green-refactor cycle of TDD
  • Red: Write a failing test first
  • Green: Write minimal code to make the test pass
  • Refactor: Improve the code while keeping tests passing
• Know how to write effective unit tests
• Know how to read a TDD unit test and understand what changes to the application are required
• Understand nested tests and how to organize test hierarchies
• Master JUnit annotations and their uses
  • @Test - Mark methods as test cases
  • @BeforeEach - Setup common test fixtures
  • @AfterEach - Clean up resources after tests
  • @BeforeAll - One-time setup before all tests
  • @AfterAll - One-time teardown after all tests
• Develop skills for writing clean, testable code

Code Example: Test-Driven Development

// 1. Write a Failing Test (Red)
@Test
void shouldAddTwoNumbers() {
    // Arrange
    Calculator calculator = new Calculator();
    
    // Act
    int result = calculator.add(2, 3);
    
    // Assert
    assertEquals(5, result);
}

// 2. Write Minimal Implementation (Green)
public class Calculator {
    public int add(int a, int b) {
        return a + b;
    }
}

// 3. Refactor (if needed)
public class Calculator {
    /**
     * Adds two integers and returns the sum.
     * 
     * @param a first operand
     * @param b second operand
     * @return the sum of the operands
     */
    public int add(int a, int b) {
        return a + b;
    }
}

// Example of @BeforeEach usage
class CalculatorTests {
    private Calculator calculator;
    
    @BeforeEach
    void setup() {
        calculator = new Calculator();
    }
    
    @Test
    void shouldAddTwoNumbers() {
        assertEquals(5, calculator.add(2, 3));
    }
    
    @Test
    void shouldHandleNegativeNumbers() {
        assertEquals(-1, calculator.add(2, -3));
    }
}