Shift-left testing in Testing Fundamentals - Test Execution Trace

Test Overview

This test simulates a simple software development process where testing starts early (shift-left). It verifies that bugs are caught early during development rather than later in production.

Test Code - unittest

Testing Fundamentals

class SoftwareDevelopmentProcess:
    def __init__(self):
        self.code_written = False
        self.tests_run = False
        self.bugs_found = 0

    def write_code(self):
        self.code_written = True

    def run_tests_early(self):
        if not self.code_written:
            raise Exception("Cannot test before code is written")
        self.tests_run = True
        # Simulate finding bugs early
        self.bugs_found = 2

    def deploy(self):
        if not self.tests_run:
            # Bugs found late
            self.bugs_found = 5

import unittest

class TestShiftLeft(unittest.TestCase):
    def test_shift_left(self):
        process = SoftwareDevelopmentProcess()
        process.write_code()
        process.run_tests_early()
        process.deploy()
        # Assert bugs found early are fewer than if tested late
        self.assertLess(process.bugs_found, 5)

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

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Create SoftwareDevelopmentProcess instance	New process object with no code written, no tests run, zero bugs found	-	PASS
2	Call write_code() to simulate writing code	Code written flag set to True	-	PASS
3	Call run_tests_early() to simulate early testing	Tests run flag set to True, bugs_found set to 2	Verify tests_run is True and bugs_found is 2	PASS
4	Call deploy() to simulate deployment	Since tests_run is True, bugs_found remains 2	Verify bugs_found is less than 5	PASS
5	Assert bugs_found < 5 to confirm early testing effectiveness	bugs_found is 2	assertLess(2, 5) passes	PASS

Failure Scenario

Failing Condition: run_tests_early() is not called before deploy(), so bugs_found remains 5

Execution Trace Quiz - 3 Questions

What does the test verify about bugs when testing is done early?

A Fewer bugs are found compared to late testing

B More bugs are found compared to late testing

C No bugs are found at all

D Bugs found are the same as late testing

Key Result

Starting testing early in the development process helps catch bugs sooner, reducing the number of bugs found later and improving software quality.