Why do you need to measure code coverage?

Code coverage is a metric that specifies how much of your codebase is covered by tests. It lets you know which parts of your code are tested and which need additional testing. 

In a previous article, we’ve seen how this metric can impact people in 5 different roles. We’ve also discussed different code coverage types and saw that a well-tested codebase is usually (but not always) a well-structured codebase.

You should prioritize code coverage to maintain and improve your overall code quality. But if you are still unsure why, in this article, we’ll explore 6 reasons for you and your team to start tracking code coverage. So let’s dive in!

Know which parts of your codebase are covered by tests

With code coverage, you can make sure you have tests in all of the critical parts of your code and guarantee that each part is well-tested. Plus, you can identify the parts of your code where there are no tests, allowing you to add tests exactly where you need them.

This visibility on the state of your code is extremely useful, especially when the codebase and the developers’ team start to grow. With code coverage, you’ll guarantee you don’t forget any part of your code.

Maintain the test quality over a project’s lifecycle

Imagine you’re working on a new piece of code but forgot to add tests, and you then create a Pull Request. If you incorporate code coverage into your build pipeline with a tool like Codacy Quality, you’ll notice that code coverage has dropped in that PR.

So what are you going to do with this information? Well, you’re most likely going to add the missing tests so that your code doesn’t cause a decrease in code coverage. Code coverage helps you maintain your code’s test quality over time.

On the other hand, if there were no code coverage in the build pipeline, all would look good, and you probably ship the code due to a lack of visibility in code coverage.

Promote a culture of writing unit tests

Code coverage helps promote a culture of writing tests. For example, you and your team can set the following standards:

• The codebase should be at least 80% covered by tests;
• Get warnings when code coverage drops below 80%;
• Block the PR when its code coverage is below 80%.

With Codacy Quality, you can automatically monitor and enforce these standards with the gates and thresholds that better fit your team. This monitoring is practical when you want to use Continuous Integration to your advantage by closely examining code coverage and ensuring that every PR comes with the necessary tests.

Increase confidence when changing code

High code coverage gives you more confidence when updating critical libraries or making a risky refactoring in the code. If your code coverage does not decrease and the behavior of the tests remains the same, you have more confidence that your code will not cause a break. 

This is especially important when working on a large codebase, where making changes can be difficult and time-consuming. High code coverage gives you more assurance that new features will not break existing ones, and it’s easier to refactor code without worrying about how the changes may negatively impact other parts of the codebase.

Code coverage is potentially important to investors

Some companies depend on investors for funding, especially in the early days. However, depending on the investment volume, some investors might want to audit the product from different perspectives. 

The audits might include checking for security vulnerabilities, performance, tests, and code coverage. As such, having a higher code coverage is a good sign during potential investment rounds.

High code coverage improves user experience and retention

Finally, code coverage can improve the user’s experience with your final product. A well-tested product is generally more stable and reliable, with fewer issues degrading the end-user experience.

Plus, with the aid of code coverage, developers can focus on areas of the code that need urgent improvement. This way, your team will be reducing and preventing bug-related user frustration. Ultimately, this will help you increase loyalty and improve user retention.