Quality metrics and measurement in Software Engineering - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a quality metric in software engineering?

A quality metric is a standard of measurement used to assess the quality of software products or processes. It helps quantify attributes like reliability, maintainability, and performance.

beginner

Name three common quality metrics used in software development.

Common quality metrics include:
1. Defect Density (number of defects per size of code)
2. Code Coverage (percentage of code tested)
3. Mean Time To Failure (average time software runs before failing).

beginner

Why is measurement important in software quality management?

Measurement provides objective data to evaluate software quality. It helps identify problems early, track improvements, and make informed decisions to enhance the software development process.

intermediate

What does 'Defect Density' measure?

Defect Density measures the number of defects found in a software module divided by its size (usually lines of code). It indicates the quality level of the code; lower values mean better quality.

intermediate

How can code coverage improve software quality?

Code coverage shows how much of the software code is tested by automated tests. Higher coverage means more code is checked for errors, reducing the chance of bugs in the final product.

Which metric measures the number of defects per size of code?

A Mean Time To Failure

B Code Coverage

C Defect Density

D Response Time

Defect Density counts defects relative to code size, helping assess code quality.

What does code coverage indicate?

A User satisfaction level

B Number of defects found

C Time taken to fix bugs

D Percentage of code tested

Code coverage shows how much code is executed during testing.

Why is measuring software quality important?

A To objectively evaluate and improve software

B To guess the number of users

C To increase software size

D To avoid testing

Measurement helps make informed decisions to improve software quality.

Mean Time To Failure (MTTF) measures:

A Average time software runs before failing

B Number of defects per line of code

C Percentage of code tested

D Time taken to write code

MTTF shows reliability by measuring how long software operates without failure.

Which of these is NOT a quality metric?

A Defect Density

B Number of developers

C Code Coverage

D Mean Time To Failure

Number of developers is not a metric for software quality.

Explain what quality metrics are and why they matter in software development.

Think about how we check if software is good or needs improvement.

Describe how defect density and code coverage help improve software quality.

Consider how counting defects and testing code parts helps find and fix problems.

Practice

1. What is the main purpose of quality metrics in software engineering?

easy

A. To manage project budgets

B. To write code faster

C. To measure and improve software quality

D. To design user interfaces

Solution

1. Step 1: Understand what quality metrics measure

   Quality metrics provide numbers that show how good or bad software quality is.

2. Step 2: Identify the main goal of using these metrics

   They help find problems and track improvements in software quality.

3. Final Answer:

   To measure and improve software quality -> Option C

4. Quick Check:

   Quality metrics = measure and improve quality [OK]

Hint: Quality metrics measure software quality, not speed or cost [OK]

Common Mistakes:

• Confusing quality metrics with project management tools
• Thinking metrics speed up coding directly
• Mixing quality metrics with design tasks

2. Which of the following is a correct example of a software quality metric?

easy

A. user interface color

B. number of developers

C. programming language used

D. defect density

Solution

1. Step 1: Identify what counts as a quality metric

   Quality metrics are measurable numbers related to software quality, like defects per size.

2. Step 2: Check each option

   Defect density counts defects per size, so it is a quality metric. Others are not numeric quality measures.

3. Final Answer:

   defect density -> Option D

4. Quick Check:

   Defect density = quality metric [OK]

Hint: Look for measurable numbers related to software quality [OK]

Common Mistakes:

• Choosing non-numeric attributes like color or language
• Confusing team size with quality metric
• Ignoring the need for measurement

3. Given a software module with 50 defects found in 10,000 lines of code, what is the defect density?

medium

A. 0.005 defects per line

B. 0.5 defects per line

C. 5 defects per line

D. 0.05 defects per line

Solution

1. Step 1: Understand defect density formula

   Defect density = Number of defects / Lines of code.

2. Step 2: Calculate defect density

   50 defects / 10,000 lines = 0.005 defects per line. This equals 0.005, which is 0.005 defects per line.

3. Final Answer:

   0.005 defects per line -> Option A

4. Quick Check:

   50 ÷ 10,000 = 0.005 [OK]

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

Common Mistakes:

• Multiplying instead of dividing
• Mixing decimal places
• Confusing defect density with total defects

4. A team tracks test coverage but reports it as 150%. What is the likely error?

medium

A. Test coverage calculation is incorrect or data is wrong

B. Test coverage can exceed 100% if tests overlap

C. Test coverage is not a valid quality metric

D. Test coverage measures defects, not code tested

Solution

1. Step 1: Understand test coverage limits

   Test coverage measures percentage of code tested, max 100%.

2. Step 2: Analyze reported value

   150% is impossible, so calculation or data must be wrong.

3. Final Answer:

   Test coverage calculation is incorrect or data is wrong -> Option A

4. Quick Check:

   Test coverage ≤ 100% [OK]

Hint: Test coverage cannot be more than 100% [OK]

Common Mistakes:

• Believing coverage can exceed 100%
• Confusing coverage with defect count
• Ignoring data errors

5. A project has these metrics: defect density = 0.02, average repair time = 5 hours, test coverage = 80%. Which action best improves overall software quality?

hard

A. Ignore defect density and focus on coding speed

B. Increase test coverage to find more defects early

C. Reduce repair time without changing testing

D. Decrease test coverage to save time

Solution

1. Step 1: Understand the impact of each metric

   Higher test coverage helps find defects early, reducing defect density over time.

2. Step 2: Evaluate options for improving quality

   Increasing test coverage is the best way to improve quality by catching defects early.

3. Final Answer:

   Increase test coverage to find more defects early -> Option B

4. Quick Check:

   More test coverage = better defect detection [OK]

Hint: More test coverage usually improves quality by catching defects early [OK]

Common Mistakes:

• Focusing only on repair time
• Ignoring defect density
• Reducing test coverage to save time