Why different testing levels catch different bugs in Testing Fundamentals - Test Execution Impact

Test Overview

This test simulates how different testing levels (unit, integration, system) catch different types of bugs. It verifies that bugs found at each level match the expected bug type.

Test Code - unittest

Testing Fundamentals

import unittest

class BugDetectionTest(unittest.TestCase):
    def test_unit_level_bug(self):
        bug_found = 'logic error'
        self.assertEqual(bug_found, 'logic error')

    def test_integration_level_bug(self):
        bug_found = 'interface mismatch'
        self.assertEqual(bug_found, 'interface mismatch')

    def test_system_level_bug(self):
        bug_found = 'performance issue'
        self.assertEqual(bug_found, 'performance issue')

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

Execution Trace - 4 Steps

Step	Action	System State	Assertion	Result
1	Test starts and runs test_unit_level_bug	Unit test simulates finding a logic error in code	Check bug_found equals 'logic error'	PASS
2	Runs test_integration_level_bug	Integration test simulates finding interface mismatch between modules	Check bug_found equals 'interface mismatch'	PASS
3	Runs test_system_level_bug	System test simulates finding performance issue in full system	Check bug_found equals 'performance issue'	PASS
4	All tests complete	All bug types correctly detected at their testing levels	-	PASS

Failure Scenario

Failing Condition: Bug type does not match expected value at a testing level

Execution Trace Quiz - 3 Questions

Which testing level is best at catching logic errors inside a single function?

A Unit testing

B Integration testing

C System testing

D Acceptance testing

Key Result

Different testing levels focus on different parts of the software, so they catch different types of bugs. Unit tests catch small code errors, integration tests catch problems between parts, and system tests catch issues in the whole system.