Defect density and detection rate in Testing Fundamentals - Test Execution Trace

Test Overview

This test calculates defect density and detection rate for a software module. It verifies that the calculations match expected values based on given defect counts and lines of code.

Test Code - unittest

Testing Fundamentals

import unittest

class TestDefectMetrics(unittest.TestCase):
    def test_defect_density_and_detection_rate(self):
        total_defects_found = 25
        total_lines_of_code = 5000
        total_defects_reported = 30

        # Calculate defect density (defects per 1000 lines of code)
        defect_density = total_defects_found / (total_lines_of_code / 1000)

        # Calculate detection rate (percentage of defects found vs reported)
        detection_rate = (total_defects_found / total_defects_reported) * 100

        # Assert defect density is as expected
        self.assertAlmostEqual(defect_density, 5.0, places=2)

        # Assert detection rate is as expected
        self.assertAlmostEqual(detection_rate, 83.33, places=2)

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

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test starts	Test framework initializes and prepares to run test_defect_density_and_detection_rate	—	PASS
2	Assign total_defects_found = 25, total_lines_of_code = 5000, total_defects_reported = 30	Variables set with given values	—	PASS
3	Calculate defect_density = 25 / (5000 / 1000) = 5.0	defect_density calculated as 5.0 defects per 1000 lines	—	PASS
4	Calculate detection_rate = (25 / 30) * 100 = 83.33	detection_rate calculated as 83.33%	—	PASS
5	Assert defect_density equals 5.0 within 2 decimal places	defect_density is 5.0	defect_density == 5.0	PASS
6	Assert detection_rate equals 83.33 within 2 decimal places	detection_rate is 83.33	detection_rate == 83.33	PASS
7	Test ends successfully	All assertions passed, test completes	—	PASS

Failure Scenario

Failing Condition: If defect_density or detection_rate calculations do not match expected values

Execution Trace Quiz - 3 Questions

What does the test verify about defect density?

A It checks defect density equals 5 defects per 1000 lines of code

B It checks defect density is less than 10

C It checks defect density is a whole number

D It checks defect density equals total defects found

Key Result

Always verify calculations of quality metrics like defect density and detection rate with precise assertions to catch errors early.

Practice

1. What does defect density measure in software testing?

easy

A. Percentage of passed test cases

B. Total number of test cases executed

C. Number of defects per size of software

D. Time taken to fix defects

Solution

1. Step 1: Understand the definition of defect density

   Defect density is defined as the number of defects found divided by the size of the software (e.g., lines of code or function points).

2. Step 2: Compare options with the definition

   Only Number of defects per size of software correctly describes defect density as defects per size of software.

3. Final Answer:

   Number of defects per size of software -> Option C

4. Quick Check:

   Defect density = Defects / Size [OK]

Hint: Defect density = defects divided by software size [OK]

Common Mistakes:

• Confusing defect density with total defects
• Mixing defect density with test case count
• Thinking defect density measures fix time

2. Which formula correctly calculates the detection rate during testing?

easy

A. (Number of defects found) / (Total defects present)

B. (Total defects present) / (Number of defects found)

C. (Number of test cases passed) / (Total test cases)

D. (Number of defects fixed) / (Number of defects found)

Solution

1. Step 1: Recall detection rate meaning

   Detection rate measures how many defects testing finds out of all defects present.

2. Step 2: Match formula to definition

   (Number of defects found) / (Total defects present) correctly shows detection rate as defects found divided by total defects present.

3. Final Answer:

   (Number of defects found) / (Total defects present) -> Option A

4. Quick Check:

   Detection rate = Found / Total [OK]

Hint: Detection rate = defects found ÷ total defects [OK]

Common Mistakes:

• Reversing numerator and denominator
• Confusing detection rate with pass rate
• Using fixed defects instead of found defects

3. A software module has 5000 lines of code and 25 defects found. What is the defect density?

medium

A. 0.5 defects per line

B. 0.05 defects per line

C. 2 defects per line

D. 0.005 defects per line

Solution

1. Step 1: Apply defect density formula

   Defect density = Number of defects / Size of software = 25 / 5000.

2. Step 2: Calculate the value

   25 divided by 5000 equals 0.005 defects per line.

3. Final Answer:

   0.005 defects per line -> Option D

4. Quick Check:

   25 ÷ 5000 = 0.005 [OK]

Hint: Divide defects by lines of code for defect density [OK]

Common Mistakes:

• Multiplying instead of dividing
• Using wrong units or decimal places
• Confusing defect density with total defects

4. During testing, 40 defects were found but the total defects present were 50. The detection rate was calculated as 1.25. What is the error?

medium

A. Detection rate cannot be greater than 1

B. Detection rate should be less than 0.5

C. Detection rate equals defects fixed, not found

D. Detection rate is unrelated to defects

Solution

1. Step 1: Understand detection rate limits

   Detection rate is defects found divided by total defects, so it must be between 0 and 1.

2. Step 2: Check given value

   Given detection rate is 1.25, which is greater than 1, so it is invalid.

3. Final Answer:

   Detection rate cannot be greater than 1 -> Option A

4. Quick Check:

   Detection rate ≤ 1 [OK]

Hint: Detection rate max is 1 (100%) [OK]

Common Mistakes:

• Allowing detection rate > 1
• Mixing detection rate with fixed defects
• Ignoring ratio limits

5. A project has 10,000 lines of code with 80 defects found during testing. Later, 20 more defects were discovered after release. What is the updated defect density and detection rate?

hard

A. Defect density: 0.008; Detection rate: 1.0

B. Defect density: 0.01; Detection rate: 0.8

C. Defect density: 0.01; Detection rate: 1.0

D. Defect density: 0.008; Detection rate: 0.8

Solution

1. Step 1: Calculate total defects and defect density

   Total defects = 80 found + 20 discovered = 100. Defect density = total defects / lines of code = 100 / 10,000 = 0.01.

2. Step 2: Calculate detection rate

   Detection rate = defects found / total defects = 80 / 100 = 0.8.

3. Step 3: Match calculations to options

   Defect density is 0.01 and detection rate is 0.8, but Defect density: 0.008; Detection rate: 0.8 shows defect density as 0.008 which is incorrect. Defect density: 0.01; Detection rate: 0.8 shows correct defect density but detection rate 0.8. Defect density: 0.008; Detection rate: 0.8 has defect density 0.008 which is wrong. Defect density: 0.01; Detection rate: 0.8 matches defect density 0.01 and detection rate 0.8 correctly.

4. Final Answer:

   Defect density: 0.01; Detection rate: 0.8 -> Option B

5. Quick Check:

   Defect density = 100/10000=0.01; Detection rate = 80/100=0.8 [OK]

Hint: Add all defects for density; found ÷ total for detection rate [OK]

Common Mistakes:

• Using only found defects for defect density
• Ignoring defects found after release
• Mixing detection rate numerator and denominator