Why white-box testing examines code internals in Testing Fundamentals - Test Execution Impact

Test Overview

This test simulates a white-box testing scenario where the tester checks the internal logic of a simple function. It verifies that the function behaves correctly for given inputs by examining its code paths.

Test Code - unittest

Testing Fundamentals

import unittest

# Function to test: returns True if number is even, else False
def is_even(num):
    if num % 2 == 0:
        return True
    else:
        return False

class TestIsEven(unittest.TestCase):
    def test_even_number(self):
        self.assertTrue(is_even(4))

    def test_odd_number(self):
        self.assertFalse(is_even(5))

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

Execution Trace - 6 Steps

Step	Action	System State	Assertion	Result
1	Test starts	Test runner initialized, test cases loaded	-	PASS
2	Calls is_even(4)	Function executes with input 4	Checks if 4 % 2 == 0, returns True	PASS
3	Asserts that is_even(4) returns True	Assertion compares returned value True with expected True	assertTrue passes	PASS
4	Calls is_even(5)	Function executes with input 5	Checks if 5 % 2 == 0, returns False	PASS
5	Asserts that is_even(5) returns False	Assertion compares returned value False with expected False	assertFalse passes	PASS
6	Test ends	All test cases executed successfully	-	PASS

Failure Scenario

Failing Condition: Function returns incorrect result for input (e.g., is_even(4) returns False)

Execution Trace Quiz - 3 Questions

What does the test check inside the is_even function?

A If the number is divisible by 2 without remainder

B If the number is greater than 2

C If the number is positive

D If the number is less than 10

Key Result

White-box testing examines the internal code logic to ensure each decision path works correctly, which helps catch errors that black-box testing might miss.