Disadvantages of Code Coverage as a Measurement

Code coverage is often used as a metric to assess how much of the codebase is tested by automated tests. While it provides valuable insights, it also has limitations that can lead to potential issues if relied upon too heavily as a measure of test quality.

Exam Question

What are some disadvantages of code coverage as a measurement for how well a system or product is tested?
(choose the best three answers)
A. It is too complicated to explain to management.
B. It could create incentives to write tests that simply increase code coverage, rather than tests that find bugs without increasing coverage.
C. Developers could stop adding more valuable tests once the target coverage is achieved.
D. It does not ensure that the most important or highest risk areas of the code are being exercised by tests.
E. It only provides insights to programmers.

Correct Answers

B. It could create incentives to write tests that simply increase code coverage, rather than tests that find bugs without increasing coverage.
C. Developers could stop adding more valuable tests once the target coverage is achieved.
D. It does not ensure that the most important or highest risk areas of the code are being exercised by tests.

Explanation

Correct Answers

B. It could create incentives to write tests that simply increase code coverage, rather than tests that find bugs without increasing coverage:
One of the main disadvantages of using code coverage as a metric is that it may incentivize developers to write superficial tests that only serve to increase the coverage percentage without actually testing meaningful scenarios. This can lead to a false sense of security, as the tests may not be effective in finding bugs.

C. Developers could stop adding more valuable tests once the target coverage is achieved:
When a specific code coverage percentage is set as a goal, developers might stop writing additional, valuable tests once that target is met, even if there are other important aspects of the code that still need testing. This can result in gaps in the test suite, particularly in edge cases or complex scenarios.

D. It does not ensure that the most important or highest risk areas of the code are being exercised by tests:
Code coverage measures the quantity of code executed by tests, but it does not indicate whether the most critical or high-risk areas of the code are adequately tested. High coverage numbers might be misleading if they don’t focus on the parts of the codebase that are most prone to failure or that have the greatest impact on the system.

Why the Other Options Are Less Appropriate

A. It is too complicated to explain to management:
While technical concepts like code coverage might require some explanation, this is not a significant disadvantage. Management can be informed about the purpose and limitations of code coverage in a way that is understandable, so this is not a major issue compared to other limitations of the metric.

E. It only provides insights to programmers:
While code coverage is a tool primarily used by developers, this is not inherently a disadvantage. The main issues with code coverage relate to the potential for misuse or misunderstanding of what the metric represents, rather than who it provides insights to.

Relevance to the PSD Exam

Understanding the limitations of code coverage as a measurement is important for the PSD exam, as it emphasizes the need for comprehensive and meaningful testing practices beyond just achieving a high coverage percentage.

Key Takeaways

• Code coverage can create incentives to write superficial tests that only serve to increase coverage numbers without ensuring meaningful testing.
• Relying solely on code coverage can result in neglecting valuable tests once a target coverage percentage is met.
• Code coverage does not guarantee that critical or high-risk areas of the code are adequately tested.

Conclusion

While code coverage is a useful metric, it has significant limitations and should not be relied upon exclusively to gauge the effectiveness of testing. Developers should focus on writing meaningful tests that cover the most important and high-risk areas of the code. For more information on preparing for the PSD exam, visit our Professional Scrum Developer PSD™ Exam Prep.