Understanding Code Coverage and Refactoring
When refactoring code, it’s important to ensure that the changes made do not introduce new issues or break existing functionality. Code coverage is one of the metrics used to measure the extent to which the codebase has been tested by unit tests.
Exam Question
You are asked to refactor part of the codebase for Application X. When you are done, all unit tests pass with 50% code coverage. What can you infer from this?
(choose the best answer)
A. Less than 50% of Application X functions correctly.
B. At least 50% of Application X functions correctly.
C. You did not break any existing unit tests.
D. There are no bugs present in Application X.
Correct Answer
C. You did not break any existing unit tests.
Explanation
Correct Answer
C. You did not break any existing unit tests:
Code coverage is a measure of the percentage of code that is executed by the unit tests. If all unit tests pass after refactoring, it means that the code changes did not introduce any issues that caused the existing tests to fail. However, this does not necessarily mean that the entire application functions correctly or that there are no bugs. It simply indicates that the existing tests still pass after the changes.
Why the Other Options Are Less Appropriate
A. Less than 50% of Application X functions correctly:
This option is misleading because code coverage does not directly indicate the functional correctness of the application. It only shows that 50% of the code has been exercised by the tests. Functional correctness would require more comprehensive testing beyond just coverage metrics.
B. At least 50% of Application X functions correctly:
Similar to the first option, this assumes that code coverage is directly related to functionality. While code coverage gives an idea of how much code is being tested, it does not guarantee that the code functions correctly. Code coverage alone cannot be used to make assumptions about the correctness of the application.
D. There are no bugs present in Application X:
This is an incorrect assumption because passing unit tests with 50% code coverage does not imply that the application is free of bugs. Bugs could still exist in parts of the code not covered by the tests, or even in the covered parts if the tests are not comprehensive.
Relevance to the PSD Exam
Understanding code coverage and its implications is essential for the PSD exam, as it reflects on the quality of testing and the reliability of the codebase after refactoring.
Key Takeaways
- Code Coverage: Measures the percentage of code executed by tests but does not directly indicate the functional correctness of the application.
- Passing Tests: If all unit tests pass after refactoring, it means no existing tests were broken, but this does not guarantee that the application is bug-free.
- Testing Beyond Coverage: Comprehensive testing goes beyond just achieving high code coverage; it involves ensuring that the tests effectively verify the functionality of the application.
Conclusion
Refactoring code and maintaining passing unit tests with a certain level of code coverage is a good practice, but it’s important to understand the limitations of code coverage as a metric. For more in-depth preparation for the PSD exam, visit our Professional Scrum Developer PSD™ Exam Prep.
