Improving Test Coverage: Strategies and Techniques

The growing emphasis on ensuring software quality and reliability of any software or hardware cannot be discussed without the subject of test coverage. Essentially, the higher the coverage, the lower the chance of undetected bugs slipping through. This article provides an overview and four essential steps to increase test coverage effectively while taking into account the needs and capabilities of each specific team and their product.

How to measure test coverage?

Before getting into different strategies and techniques it is important to understand where your product stands concerning test coverage. In essence, calculating test coverage involves measuring how much of a product's source code is executed during a test run. However, in most cases that is not enough to get the most relevant coverage for the whole product. There are multiple models to take into account, for example:

1. Workflow coverage
2. Functionality coverage
3. Requirements coverage
4. Risk coverage

Due to the complexity of the issue of calculating test coverage, look into getting support from external consultants who specialize in areas such as this. Once you’ve determined your current test coverage, the range needed for planning and implementing the desired target coverage becomes much more clear. 

Steps to improving test coverage

While reaching the desired target percentage of test coverage is significant, it is also important to make sure that you have targeted the most crucial areas of the product to offer your clients a safe and worthwhile product. 

Step 1: Establish priority target areas

According to the seven testing principles, testing everything is not possible in most cases, which means prioritizing testing efforts to target the most critical areas is one of the first steps to take during test coverage improvement. The best sources for uncovering these areas are:

• Stakeholders. Various stakeholders, like product owners, business analysts, developers, and many others already hold much of the information that is needed to pinpoint any areas of concern. They can provide business and development-related perspectives on the issue as well as any commercial risk areas.
• The users. It is highly valuable to also include the opinions of your user base as well as any data that has been gathered regarding their behaviors. User experience surveys provide information on what are their expectations and which areas are problematic from the user’s perspective. Gathered data (during their use of the software) illustrates the most valuable and commonly used areas. 
• Existing known issues. Bugs tend to cluster so it is good to take into account which areas are known to be more vulnerable. Determining high-risk areas is essential for planning the test coverage improvements.

After collecting knowledge from these multiple sources, you can create a prioritized list of areas. This will help focus your resources and guide the process to improve test coverage efficiently. 

Step 2: Plan and create strategies

Improving test coverage can be a very long and tedious process so it is best to plan and create strategies before starting this process. There are multiple factors to take into account to form a strategy that fits with the needs of your product:

• SDLC. The flow of the currently applied software development life cycle should be assessed and possibly alternated. To improve and maintain test coverage, the SDLC itself should include test creation and implementation in the early stages. 
• High-risk areas. Previously identified priority areas should also include high-risk areas. These areas need to be covered by testing to prevent any critical bugs from making it to production. 
• Test automation. Adding automated tests is a great way to improve and maintain test coverage. Unfortunately, it is not possible or recommended to automate all of your tests. Estimating the balance between automated and manual tests plays a big role in the improvement of test coverage as well as how resources should be allocated. 
• Resources. It is important to consider your internal team's capabilities and bandwidth. If there is a lack of either, outsourcing some of the efforts is a good option. 
• Timeframe and goals. They help establish clear expectations and direction. It is good to leave space and plan for potential setbacks, but having some kind of timeframe will make sure the goals and momentum are not lost. 

Once you’ve identified and understood these critical factors, it’s easier to determine which of the strategies would be most useful and much easier to adopt. Typically, you can use a combination of different strategies:

• Risk-based testing. Prioritize and target tests for high-risk areas. This strategy focuses limited resources on areas where failure would have the most significant impact.
• Incremental coverage goals. Set incremental, realistic goals, which allow gradual improvement without overwhelming the team or delaying deliverables. For example, 8-10% coverage improvement per sprint.
• Test-driven development (TDD). Embracing TDD enables teams to boost code dependability and support test coverage creation as well as maintenance.
• Use of code coverage tools. Utilizing tools (e.g. JaCoCo, Istanbul, SonarQube) helps track coverage levels and identify untested areas of the code.
• Collaborative testing. As mentioned above, different teams have a lot of valuable knowledge that is specific to their roles in the organization. 
• Mutation testing. It is used to design new software tests and evaluate the quality of existing software tests.

Step 3: Select applicable techniques

Now that you’ve set up a plan, it is time to get more technical. There are multiple different test techniques that you can apply to ensure more thorough testing and higher-quality code. Test techniques also help determine and improve coverage. The techniques are categorized into three different groups:

• Black-box testing
• White-box testing
• Experience-based testing

The most commonly used techniques fall under the category of black-box testing. More complex systems may benefit from advanced techniques like model-based testing or exploratory testing, while simpler systems can rely on boundary value analysis or equivalence partitioning.

Step 4: Ensure test maintenance 

Reaching the desired test coverage is no small feat, but the work doesn’t end there. With continuous product development, maintaining coverage is an ongoing effort. When you introduce new designs or features to the product, make sure any existing tests are still relevant. In addition, any new features should be assessed for the creation of new tests (including their depth). The good news is that if the test coverage maintenance is included in the SDLC and not left aside, it will be much easier than the previous steps. 

You might be interested in: Understanding Test Maintenance: Best Practices and Strategies

The bottom line

Improving test coverage is essential for delivering high-quality, reliable software that meets user expectations and withstands market demands. By understanding how to measure test coverage, prioritizing critical areas, devising tailored strategies, and employing suitable techniques, teams can methodically enhance their test coverage. Maintenance ensures that these improvements remain effective as the product evolves.

With the right approach, improving test coverage doesn't have to be overwhelming—it can be a transformative process that not only reduces risks but also builds trust in your software.