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Test Coverage vs Code Coverage: A Comparative Analysis

Author: Pricilla Bilavendran

Last updated: February 23, 2024

Test Coverage vs Code Coverage
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We constantly run around the quality outdoors without understanding internal factors that contribute to the quality of the code. In Software Development, ensuring the quality of code is of utmost importance. Test coverage and code coverage are two important concepts in software testing and commonly used metrics for measuring code quality and the effectiveness of testing. They both measure the extent to which a program’s code has been tested, but they do so in different ways.

While these terms are often used interchangeably, they have distinct differences and purposes. You can read the blog here to understand Test Coverage basics.

In this blog, we will learn more about test coverage and code coverage, how they differ from each other, and how these metrics together help us to build better software and applications. Let’s explore the details of these two terms and their relation to each other in the following sections.

 

What Is Test Coverage?

Test coverage is a measurement used to describe the degree to which the source code/requirements of an application are tested by a particular set of test cases. It is usually expressed as a percentage that measures how much of the program code has been tested.

Test coverage aims to identify areas within the codebase that have not been adequately tested, helping developers identify potential bugs or vulnerabilities.

 

What Is Code Coverage?

Code coverage focuses on measuring how much of the source code has been executed during testing. It provides insights into which lines or branches of code have been exercised by tests. Developers may use code coverage to determine the completeness and thoroughness of their test suite. You can increase the stability and maintainability of your codebase by thoroughly testing it.

 

Understanding the Differences: Test Coverage vs Code Coverage

While both metrics aim to provide insights into testing effectiveness, they differ in their scope and purpose. Test coverage primarily focuses on functional aspects, ensuring that all possible scenarios are tested while minimizing redundancy. Code coverage, on the other hand, concentrates on examining individual lines or branches within the source code.

 

Test Coverage Code Coverage
Measures the percentage of code that a test suite has run Measures the percentage of lines of code that a test suite has run.
Used to guarantee the software’s quality Used to detect the code segments that are not being tested
Helps in tracking the functional requirement coverage Helps in tracking the development feature of the application
Provides suggestions to include more test cases for better coverage Provides suggestions to improvise the code/remove unnecessary code
Analyzing only the extent to which the tests execute the code. Reveals code smells, dead code, and potential vulnerabilities.
Provides a holistic view of the coverage of requirements Provides a holistic view of the codebase, helping identify the areas for improvement

 

 

Pros and Cons of Test Coverage

Let’s see in detail the advantages and disadvantages of test coverage.

Pros:

1. Ensuring the quality of the application/system: Test coverage verifies a product or site’s quality by putting all of its features and functionalities to the test, which can increase customer satisfaction.

2. Time-Saving: Teams may save time and resources by leveraging test coverage to identify and address issues early in the development process rather than having to spend them debugging and fixing defects after the product has been released.

3. Better code quality: Before deploying code into production, test coverage enables developers to ensure that it meets quality standards and functions as intended.

4. Advanced Coding Practices: Understanding the code base better helps the developers to write code in a more structured and efficient manner.

5. Better Traceability: Test coverage provides detailed traceability of each test case/run, allowing teams to quickly understand what requirements are covered and where there are gaps.

6. Increased efficiency: Test coverage helps to measure the efficiency of the software testing process, and helps to ensure quality assurance. 

7. Increased Confidence: Testing all code helps us build a more reliable and predictable software system which gives them greater confidence in making changes to the codebase.

Cons:

1. Requires investment: The level of test coverage necessary to uncover all bugs can be quite high, and therefore incredibly expensive. It requires a lot of time, money, and resources to completely test every part of a software program. This may get expensive and challenging to handle, especially for smaller businesses.

2. Covering the combinations and edge case scenarios: As we all know, Exhaustive testing is impossible. When creating test coverage plans, it might be challenging to consider every potential edge case, which could provide unexpected outcomes when used in real-world scenarios. It becomes unreliable.

3. Difficult to spot all Bugs in the System: Some defects that arise from intricate interactions between several program components may be hard to find, even with intensive testing.

4. Provides a false sense of security: While test coverage is an indicator that suggests how thoroughly a software is tested, in most cases, it cannot guarantee the efficacy of the tests, and may even give a false sense of security. 

5. Not covering the multiple aspects of code quality: It is important also to evaluate other aspects of code quality to ensure that the software is of the highest quality. Test coverage focuses primarily on code execution, ignoring other aspects of code quality.

 


 

Pros and Cons of Code Coverage

Let’s see in detail the advantages and disadvantages of test coverage.

Pros:

1. Improves Quality and Reliability: Developers may evaluate which regions of the codebase are well-tested and which ones might need more work by looking at the code coverage. It helps developers to locate code segments that are more vulnerable.

2. Helps Identify Potential Issues: Dead code, smelly code, and possible vulnerabilities can potentially be detected via code coverage. Additionally, it can assist in finding any unexpected consequences of recent changes to the code or regression. This helps in finding defects early in the development cycle and cuts down on the time and expense of debugging.

3. Promotes Refactoring Efficiency: Code coverage provides you with an overview of the test coverage, which aids in assessing the efficacy of your refactoring. By doing this, you can reduce the possibility of introducing new defects and maximize the impact of the refactoring effort. 

4. Enriches Communication and Collaboration: Since code coverage is a quantitative metric, it facilitates effective communication between developers and stakeholders on the coverage of code tests using actual statistics. It gives stakeholders visibility so they can comprehend the scope of codebase testing.

5. Provides insights about Code Quality: Identifying the parts of the code that require work also helps, since this may serve as the foundation for the code quality improvement strategy. Developers are therefore encouraged to build more reliable and scalable code.

Cons:

1. Provides a false sense of security: Similar to the “Test Coverage” metric, this can potentially create a false sense of security. Code coverage can show the extent of testing that has been conducted, but can’t guarantee that the application is flawless.

2. Complex tool support required and Expensive: The configuration and data collection process need the use of a specialized tool, which can be complex and challenging to set up effectively. Purchasing the dynamic analytic tools needed to produce thorough information on code coverage might be costly.

3. Biased Metric: It is usually skewed in favor of the sections of the application that get more testing. Consequently, it might not be an accurate representation of the complete application.

4. Time-Consuming: The process of creating comprehensive and helpful reports might take some time. Also, it needs deeper analysis and research compared to running tests.

5. Unable to exercise all code paths: For big and complicated projects, it might not be possible to execute every code path/branch because of the time and expense required.

 

In Summary

While test coverage focuses on measuring the extent of code execution during testing, code coverage provides a broader perspective on law quality. Combining these two criteria and employing them together allows developers and stakeholders to have a deeper grasp of their codebase and make well-informed choices about enhancements and optimizations. This combined approach improves overall quality assurance practices and contributes to the delivery of reliable software results in your systems.

In conclusion, while both test and code coverages give precious insights into software quality, they differ in terms of the scope, focus areas, tools employed, and dimensions used. Understanding these differences can help us in making informed decisions regarding testing methodologies for optimal software stability and quality assurance.

 

Pricilla Bilavendran

Pricila Bilavendran is a test engineer and a certified mentor, currently at Billennium, as well as an advocate for diversity and inclusion. Her experience with Functional, EDI, ETL, Automation, API testing and Postman is part of what she shares in her workshops, webinars, and writing. A global ambassador for the WomenTech Network, and one of the speakers at its 2023 conference, she can be found on LinkedIn, Twitter, and her blog.