Defect density and detection rate in Testing Fundamentals - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Defect Density Calculation

Imagine a software module has 50 defects found during testing. The module size is 10,000 lines of code. What is the defect density?

A 0.5 defects per line of code

B 0.005 defects per line of code

C 0.05 defects per line of code

D 5 defects per line of code

💡 Hint

Defect density = Number of defects / Size of code.

Defect density is calculated by dividing the number of defects by the size of the code. Here, 50 defects / 10,000 lines = 0.005 defects per line.

🧠 Conceptual

intermediate

Calculating Defect Detection Rate

A testing team found 80 defects in the first week and 40 defects in the second week. If the total defects found after two weeks is 120, what is the defect detection rate for the second week?

A 40%

B 50%

C 66.7%

D 33.3%

💡 Hint

Defect detection rate = (Defects found in period / Total defects found) * 100%

Second week detection rate = (40 / 120) * 100% = 33.3%

❓ Predict Output

advanced

Output of Defect Density Calculation Code

What is the output of this Python code?

Testing Fundamentals

def calculate_defect_density(defects, lines_of_code):
    return defects / lines_of_code

result = calculate_defect_density(25, 5000)
print(f"Defect Density: {result:.4f}")

A Defect Density: 0.0250

B Defect Density: 0.0500

C Defect Density: 0.0050

D Defect Density: 0.0005

💡 Hint

Divide defects by lines of code and format to 4 decimals.

25 defects / 5000 lines = 0.005. Formatted to 4 decimals: 0.0050.

❓ assertion

advanced

Assertion for Defect Detection Rate

Which assertion correctly verifies that the defect detection rate is 40% when 20 defects are found out of 50 total defects?

Testing Fundamentals

defect_found = 20
total_defects = 50
detection_rate = (defect_found / total_defects) * 100

A assert detection_rate == 40

B assert detection_rate == 0.4

C assert detection_rate == 0.40

D assert detection_rate == 4

💡 Hint

Remember detection_rate is a percentage, not a fraction.

The detection_rate is (20/50)*100 = 40. So the assertion must check for 40, not 0.4.

🔧 Debug

expert

Debugging Defect Density Calculation Error

What error will this code raise when calculating defect density?

defect_count = '30'
lines_of_code = 10000
defect_density = defect_count / lines_of_code
print(defect_density)

Testing Fundamentals

defect_count = '30'
lines_of_code = 10000
defect_density = defect_count / lines_of_code
print(defect_density)

A TypeError: unsupported operand type(s) for /: 'str' and 'int'

B ZeroDivisionError: division by zero

C NameError: name 'defect_count' is not defined

D SyntaxError: invalid syntax

💡 Hint

Check the data types of variables used in division.

defect_count is a string, lines_of_code is an integer. Dividing string by int causes TypeError.

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