Module 3 Guided Project

Understanding Unit Testing

Unit testing is the process of testing individual components or units of code in isolation. A "unit" is typically a method or function that performs a specific task. The goal is to verify that each unit works correctly on its own before integrating it with other units.

The GIVEN-WHEN-THEN Pattern

This project follows the GIVEN-WHEN-THEN pattern for writing clear, focused unit tests:

• GIVEN: Set up the test conditions and initial state
• WHEN: Execute the method being tested
• THEN: Verify the expected results

Test Case Example

@Test
public void calculateTotal_withValidItems_returnsCorrectSum() {
    // GIVEN
    ShoppingCart cart = new ShoppingCart();
    cart.addItem(new Item("Book", 15.99));
    cart.addItem(new Item("Pen", 1.29));
    
    // WHEN
    double total = cart.calculateTotal();
    
    // THEN
    assertEquals(17.28, total, 0.01, "Total should be sum of all item prices");
}
                

Testing Edge Cases

A thorough test suite should include tests for edge cases such as:

• Empty collections
• Null inputs
• Boundary values
• Invalid inputs that should throw exceptions

Example Edge Case Test

@Test
public void calculateTotal_withEmptyCart_returnsZero() {
    // GIVEN
    ShoppingCart cart = new ShoppingCart();
    
    // WHEN
    double total = cart.calculateTotal();
    
    // THEN
    assertEquals(0.0, total, 0.01, "Empty cart should return zero total");
}

@Test
public void addItem_withNullItem_throwsIllegalArgumentException() {
    // GIVEN
    ShoppingCart cart = new ShoppingCart();
    
    // WHEN/THEN
    assertThrows(IllegalArgumentException.class, 
                 () -> cart.addItem(null),
                 "Adding null item should throw IllegalArgumentException");
}