What Is Test Coverage in Software Testing and Why It Deserves More of Your Attention

What is the root of quality in software? A good budget, a smart strategy, customer centricity… All are valid answers. But they would be useless without skilled execution. From a QA perspective, quality is how well you examine your app. If you check every corner of your product and make sure it all works as needed, then you’ll achieve the results you envisioned.

That’s why the value of your project is directly linked to your test coverage.

What Is Test Coverage?

Technically speaking, test coverage is a collection of metrics that determine how much of your app was investigated by your test cases.

Let’s take a look at a brief example. Imagine you’re testing a calculator app with four functions:

• Add.
• Subtract.
• Multiply.
• Divide.

You run a few tests to check if the addition and multiplication features work properly. But you haven’t tested subtraction or division yet.

This means you have low test coverage because only two of the four features (50%) have been tested. There’s still a chance that subtraction and division might have bugs. Yet, you wouldn’t know since those areas weren’t covered by your tests. To ensure high test coverage, you’d need to check all features of the calculator.

So, simply put, test coverage is about what portion of your product was investigated.

Test Coverage vs Code Coverage

Code coverage is a specific type of test coverage. It measures how much of your code is executed during testing. The point of code coverage is to make sure your tests include different parts of your code. Why is that significant?

• If a part of your code isn’t run during testing, it’s possible that errors in that part won’t be found.
• Even if you’re testing the system’s features, there could still be hidden code paths that never get checked.

So, code coverage helps you see which areas of your app are not being tested at all.

A crucial thing to remember is that good code coverage doesn’t automatically mean good test coverage. If you flip the switch and the light turns on, you can say that it works (you executed the code). But what you didn’t check is:

• Is the light too dim or too bright?
• Does the intensity of the light go down with time?
• Does the light bulb break when it’s been on for a while?
• Can you turn off the light at all?

To sum it up:

• Code coverage checks what’s run (the switch, the bulb, the wiring, etc).
• Test coverage checks how well it works under meaningful conditions.

Both of these are pivotal to your product’s quality. And prioritizing one over the other is a mistake. You can’t choose between “what to examine” and “how to examine it”. Code and test coverage are equally important and should always be viewed as interlinked entities.

How High Test Coverage Benefits Your Business

It’s nice to know what test coverage is. But what of it? This little section will explain the massive benefits test coverage offers.

But do note one thing. Test coverage becomes an advantage only when it’s high, around 80% and up. Checking ten out of a hundred features in your app is like taking a vitamin when you’re paralyzed – not much help.

So, the perks of high test coverage are that it:

• Gives you a fuller picture of your product’s quality. You can also better grasp how well your QA resources perform.
• Lets you identify which areas are well-tested and which are not. From here, you can accurately pinpoint what needs to be adjusted and what specialists should be added to the crew for refined outcomes.
• Highlights possible gaps in your testing strategy. A clear understanding of your weaknesses can help proactively address potential risks before they escalate.
• Aids in prioritizing QA services efforts. Hence, you not only improve the quality of your product but also streamline the testing process.
• Contributes to overall build quality. The more of your app is tested, the fewer bugs there are.
• Ensures that decisions are grounded in a solid understanding of the product’s quality and readiness.
• Helps resolve issues early in the development process. This prevents the accumulation of technical debt caused by shortcuts or unresolved bugs.
• Lets you fix issues as they arise, allowing for faster iterations and more confident releases. And if you make good use of automated software testing services, you can further shorten the SDLC.
• Builds trust with your users. When customers know they can rely on your product to perform correctly, they are more likely to remain loyal and recommend it to others.
• Yields long-term returns by reducing the costs associated with fixing bugs post-release. In other words, high test coverage advances your ROI.

As you can see, test coverage is not just something QA engineers use for their processes. It can give meaningful insights into your quality assurance, upgrade project value, and advance your business.

Challenges in Ensuring Proper Test Coverage

Before we go into details on how to ensure good test coverage and how to work with test coverage metrics, we should address something.

The trickiest thing about securing high coverage is finding talent who can do so. You can have millions of test cases that still result in poor coverage. Or your team may decide to go for 100% test coverage without realizing that it’s often wasteful and unnecessary.

So, if you don’t have a skilled crew, you’re very likely to run into some troubles.

• Tight deadlines and limited resources can prevent you from establishing thorough coverage. And a lack of skilled personnel may hinder the creation of effective tests.
• Complex applications can make it challenging to identify relevant test scenarios. You can end up with inadequate or poorly defined cases that don’t cover critical functionality.
• Without a solid understanding of the business context, your crew may overlook essential features, misinterpret requirements, and fail to recognize key risks.
• Relying on third-party services or APIs can complicate testing. Changes or failures in these components may impact how your app behaves, making it hard to achieve reliable coverage.
• Frequent updates and changes to the codebase require continuous adjustments to test cases. Keeping high coverage where everything shifts all the time is something not many specialists can do.
• Focusing solely on achieving high test coverage can lead to neglecting other vital aspects of testing. In such cases, performance, security, and usability may be compromised.
• An excessive focus on test coverage metrics can lead to superficial testing. Your team may prioritize numbers over meaningful test scenarios that ensure quality.

Overall, before doing anything, you need to make sure you have the right specialists. That’s the number one rule for achieving triumph with your product in all its aspects.

How to Measure Test Coverage

To understand how well your test cases perform, you need to analyze your test coverage percentage. There are quite a few ways to do so.

• Manual tracking. Developers can manually log which lines, branches, and conditions have been executed while running tests.
• Code reviews. You can hold code reviews where peers manually check if sufficient test cases exist for various parts of the code.
• Test case mapping. You can also map test cases directly to specific code sections and features manually, creating a checklist of areas covered.
• Test coverage tools. Your team can employ software that tracks which parts of the code were executed during testing.

As you can imagine, the last option is the most common. Test coverage tools are simple to use. They are also quick and more accurate compared to other methods. But they may make mistakes. For example, with dynamic code execution, exception handling, asynchronous code, etc., test coverage tools might miss some bits of the code.

So, you shouldn’t dismiss manual testing services for good test coverage right away.

Using Different Types of Testing Coverage Techniques

You can also understand where your tests lack by using a variety of coverage techniques. These act as divisions of test coverage, handling different parts of your software (code, features, user requirements, etc). And when you combine them, you get a holistic perspective on your overall coverage.

• Product coverage measures the extent to which different parts or features of a product are tested.
• Risk coverage focuses on testing areas of the product that carry the most risk, such as critical functionalities or areas prone to failure.
• Requirements coverage measures the percentage of product requirements that are covered by test cases.
• Compatibility coverage assesses how thoroughly a product is tested across various devices, browsers, operating systems, and environments.
• Boundary value coverage tests the boundaries or limits of input ranges (e.g., minimum/maximum values, just inside/outside boundary conditions).
• Branch coverage measures the percentage of decision branches (e.g., if-else statements) that are tested.
• Statement coverage tracks the percentage of executable statements in the code that are executed by the test cases.
• Path coverage measures whether all possible paths through the code’s control flow (the path the program takes during execution) have been tested.
• Condition coverage tests each boolean condition (true/false) within decision points.

The above are also often called test case coverage metrics. From them, you can calculate the total coverage percentage. There’s a bit of confusion when it comes to defining these metrics. And it’s quite common to mix them up with types or techniques to ensure decent code coverage.

Examples of Test Coverage Metrics

To make sure you don’t join this puzzled party, let’s take a look at a few test coverage metrics examples.

Test design coverage metrics focus on how well the test design covers various elements of the software, such as functionality, risk, and scenarios. This includes:

• Boundary value coverage.
• Decision/branch coverage.
• Equivalence partitioning coverage, etc.

So, these metrics help assess the quality of test design.

Test coverage metrics in Agile are used to ensure that testing keeps pace with the continuous development and delivery cycle. These metrics help track the progress and completeness of testing within sprints. They typically focus on:

• User story coverage.
• Sprint test coverage.
• Acceptance criteria coverage.

Here, test coverage metrics are aimed at making sure the tests are aligned with the iterative nature of the methodology.

Test automation coverage metrics assess the extent to which automated tests cover the codebase, functionalities, and scenarios. They let you track how much of the testing process is automated. Key metrics include:

• Automated test case coverage.
• Automated regression test coverage.
• Automated code coverage.

From all that, you can see that test coverage metrics in software testing can be very different and relate to various concepts. Yet, they all have a single purpose. They act as quantifiable measurements used to assess something. Returning to our original test coverage metrics (risk, product, compatibility coverage, etc.), they simply allow you to generalize the overall coverage of your app.

Defining Your Sufficient Test Coverage

Now that we’re done with this little test coverage fallacy, let’s move on to a more significant aspect. Specifically, you need to know how to establish your own “good coverage”.

Understand Product Risks

Begin by assessing the risks associated with the product. Identify which areas are critical for functionality, user experience, security, and business success. Higher-risk components require more thorough testing, while less risky ones might need lighter coverage.

Ask questions like:

• What are the most business-critical features?
• What kind of defects would cause the most harm?
• Are there any parts that users will heavily interact with?

Identify Testing Goals

Align coverage with your business goals. If the product must be delivered rapidly, you’ll focus on critical functionality. If reliability is key, comprehensive testing becomes a priority. Define the scope of what “sufficient” means in terms of customer expectations and product stability.

Testing goals can include:

• High coverage for user-facing functionality.
• Adequate security and performance testing for key features.
• Compliance with industry standards (e.g., medical, financial sectors).

Set Benchmarks Using Test Coverage Metrics

Utilize different test coverage metrics to quantify how much of the code or functionality is being tested. Depending on the nature of the product, aim for:

• 80-90% coverage for critical functionality.
• 70-80% coverage for overall code or branches.

Keep in mind that 100% code coverage doesn’t always guarantee a bug-free product. Focus on handling important use cases rather than aiming for arbitrary numbers.

Map Requirements to Test Cases

Map test cases to requirements, user stories, or features. Ensure that each requirement has corresponding test cases to verify it. This helps achieve functional coverage and ensure that the product meets the intended functionality and the user’s expectations.

Iterate & Reassess Coverage

Sufficient coverage is not static. It evolves as the product grows. Continuously assess coverage after each sprint or release to ensure that newly introduced features are tested and existing test cases are updated as needed.

Use feedback from production environments (e.g., bugs found in production) to identify areas that may need better coverage.

Use Industry Standards as a Reference

Look at industry standards or similar companies in your domain for coverage benchmarks. While every product has unique needs, industry benchmarks can serve as a baseline for defining sufficient coverage.

Overall, remember that good test coverage doesn’t mean running a lot of tests. You can have relatively few cases that handle a big portion of your product. It’s just a matter of finding experts who can design tests with ample reach.

Signs that Your Test Coverage Is Lacking

Speaking of the importance of skills for test coverage, let’s also take a look at poor coverage markers. If you observe any of the below troubles in your project, it’s time to revamp your QA processes.

• Frequent or severe bugs reported by users after releases.
• Tests that often fail for unclear reasons or provide inconsistent results.
• New features that are deployed without corresponding test cases or documentation.
• No clear mapping between requirements and test cases.
• Frequent code changes or refactoring without associated tests.
• Lack of test metrics that help track and analyze test coverage.
• Dependency on bug reports for QA rather than proactive testing.
• Changes in code that often result in unexpected behavior or bugs.
• Test cases that don’t reflect current requirements or app behavior.

Alright. Enough about the bad.

How to Improve Your Test Coverage

Let’s finish on a positive note. And a useful one. We’ll discuss real-life practices that help you advance your test coverage.

Try Test Coverage Analysis

Test coverage analysis in software engineering is used to evaluate the effectiveness of your QA efforts. It’s not calculating the percentage of the coverage. 40% is clearly not good, so what now?

Test coverage analysis is about dissecting the metrics you use to locate the root cause of poor results. Maybe your code could be better, perhaps your QA engineers need to upskill, could be that your overall testing strategy is disorganized – insufficient test coverage can result from thousands of reasons.

The point is to find out why and establish a remedy plan. And that’s the true value of test coverage analysis. It lets you:

• Identify gaps in testing.
• Organize testing efforts.
• Enhance resource allocation.
• Advance the decision-making process.
• Improve software quality.

And you don’t really have to pay money for specialized tools or expertise. All you need is to get your team together, gather their perspectives and insights, and use data from your development to evaluate your project. Of course, you can always partner with a QA company. An objective, unbiased investigation holds a lot of value on its own. But it’s definitely not obligatory.

Use These Test Coverage Tips

Lastly, here are a few tips from our QA experts on how to improve your test coverage. The QA Madness team has worked with hundreds of clients. And we’ve nailed down the best practices that bring in refined results.

• Write clean and organized code. It’ll be easier to maintain and understand, making it simpler to identify which areas need testing.
• Use a combination of testing types. A mix of unit, integration, and end-to-end tests will result in comprehensive coverage.
• Test your software across various devices and platforms. Expanding your testing scope helps identify potential issues that could arise in real-world use.
• Assess how modifications might impact your existing test coverage. Understanding the potential effects helps you proactively adjust your testing strategy.
• Focus your testing efforts on the most important and high-risk features. Risk-based prioritization ensures that critical functionalities are thoroughly tested, even if your overall coverage percentage is lower.
• Aim for meaningful test cases rather than just increasing the number of tests. Strive to create high-quality tests that effectively validate critical functionalities. And don’t for a large number of superficial tests that do not provide real insights into the software’s behavior. You can find out more on how to create functional tests that matter in our blog.
• Regularly review and update your tests to ensure they remain relevant and effective. This ongoing maintenance helps prevent coverage gaps.
• Encourage collaboration between stakeholders. Sharing insights about the codebase can lead to better understanding and coverage.
• Automate repetitive testing tasks to save time and reduce human error. It’ll increase the overall accuracy of your test cases.
• Keep track of your test coverage metrics over time to identify trends and areas for improvement.

Last but not least, assemble a team that can correctly execute your vision. No matter how bulletproof your plan is, without skilled experts, it’ll be no more than a fancy document.

To Sum Up

Test coverage is an incredibly valuable asset. It’s not another “QA mumbo jumbo”, as some may put it. Test coverage is useful in many ways. And it can help your team and your business create a targeted improvement strategy. You only need to know how to work with it.

So, we hope this article helped you better grasp this practice. And if you want to turn test coverage into its true powerhouse form – our team is always here.