Why white-box testing examines code internals in Testing Fundamentals - Automation Benefits in Action

Verify white-box testing inspects code internals

Preconditions (2)

Step 1: Open the source code of the function 'calculate_discount' that applies a discount based on customer type

Step 2: Write a test that checks the function behavior for different customer types by inspecting internal logic branches

Step 3: Run the test and observe if all code paths are covered and verified

✅ Expected Result: The test should confirm that all internal branches of the function are tested and behave as expected

Automation Requirements - unittest

Assertions Needed:

assertEqual to verify function output for each input

assertTrue to confirm internal conditions if accessible

Best Practices:

Use clear and descriptive test method names

Test all logical branches inside the function

Keep tests independent and repeatable

Automated Solution

Testing Fundamentals

import unittest

# Function to test

def calculate_discount(customer_type, amount):
    if customer_type == 'regular':
        return amount * 0.9  # 10% discount
    elif customer_type == 'vip':
        return amount * 0.8  # 20% discount
    else:
        return amount  # no discount

class TestCalculateDiscount(unittest.TestCase):
    def test_regular_customer(self):
        self.assertEqual(calculate_discount('regular', 100), 90)

    def test_vip_customer(self):
        self.assertEqual(calculate_discount('vip', 100), 80)

    def test_unknown_customer(self):
        self.assertEqual(calculate_discount('guest', 100), 100)

if __name__ == '__main__':
    unittest.main()

This test script uses Python's unittest framework to check the calculate_discount function.

Each test method checks a different internal branch of the function: 'regular', 'vip', and unknown customer types.

Assertions verify the output matches expected discounts, ensuring the internal logic is tested.

This approach shows white-box testing by directly examining and validating the code's internal decision paths.

Common Mistakes - 3 Pitfalls

Testing only one input without covering all branches

Using print statements instead of assertions

Not isolating tests leading to dependencies

Bonus Challenge

Now add data-driven testing with 3 different customer types and amounts

Show Hint