Test Coverage vs Code Coverage: Everything You Need to Know

For software developers and testers, quality code is at the very essence of their work. An application’s source code is its skeletal system. If something is amiss in an application’s source code, it will cause issues all along the production process — affecting both software developers and testers alike. 

The question lies in coverage: Should you focus on test coverage or code coverage? While they are related, there are differences between the two. And knowing those differences will help you prioritize within your testing strategy. 

In this blog, we will discuss the differences and similarities between test coverage vs code coverage, what the purpose of each is, and their limitations and advantages. 

What is Code Coverage?

Code coverage is a measurement of the amount of an application’s source code that has been executed during testing. It tells you what code has and has not been tested. It can be a helpful tool to identify what parts of code in need of testing remain. 

Test coverage is critical in order to uncover errors in your source code. The internal structure of the code depends on it! White-box testing, for example, examines how the code is structured and how it will impact the development process. 

Measuring code coverage can come in the form of a percentage of the total number of lines of code executed during testing. 

Related Reading: 2023 Test Coverage Guide 

Code Coverage Advantages

You want to determine the quality of your tests, right? By leveraging code coverage, you can expect: 

• Shortened development cycles due to test focus centered on critical parts of code. 

• Increased software reliability. 

• Enhanced code quality. 

• More rapid debugging process. 

• Confidence in your codebase. 

Code Coverage Disadvantages

Like any tool in your testing toolkit, there can be some drawbacks when using code coverage. These include: 

• The quality of your code may not always be reflected by code coverage. Code coverage does not necessarily equate to code quality. 

• Superior code coverage does not reflect the quality of your tests. You could have excellent code coverage yet still be hampered by inefficient tests. 

• Relatedly, while you may have superior code coverage, your code could still contain errors. Code coverage does not absolve you of code errors. 

• Code coverage can be time-consuming and costly — especially if different code coverage tools are required for different programming languages. 

This all boils down to one thing. At its core, code coverage helps reduce the chances of there being issues within your code by ramping up the number of potential code test executions. Code coverage is your spotlight — what you do with that spotlight goes a long way in benefiting your code. 

What is Test Coverage?

Test coverage quantifies how many of the various application’s features are being tested. This is a good indicator of risk. Maintaining quality test coverage is important for ensuring software quality while identifying any software defects. 

While code coverage is viewed through the lens of internal code structure, test coverage is viewed through the lens of the end user. Test coverage helps identify whether all necessary scenarios and use cases have been considered in order to detect any potential issues. 

Test coverage is measured by various metrics that include specifications, risk, functionality, and product. 

Test Coverage Advantages

Test coverage can help developers and testers in a multitude of ways, including: 

• Reduces the risk of new defects while ensuring current issues are found and fixed. 

• Enhances quality of software by providing a thorough assessment of the software’s functionality. 

• Identifies what portions of an application have yet to be tested to ensure validation. 

• Simplifies the process because it does not require technical code knowledge. 

• Boosts confidence in the application because it ensures every aspect has been properly reviewed. 

• Saves time and money by rooting out bugs that could otherwise show up later on during the development process. 

Test Coverage Disadvantages

Similar to code coverage, test coverage — while providing invaluable insight into application functionality — has its shortcomings: 

• The scope of your test coverage is limited by your team’s available resources. 

• Test coverage does not guarantee your application’s code is free of bugs. 

• Test coverage is intrinsically linked to the quality of your tests; if you have substandard tests, your test coverage will also be substandard.