Types of Defects in Software Testing

“It’s not a defect, it’s a feature!” is a common discussion that ensues between testers and developers when the latter debates their stance on a finding with the former. After a lot of back and forth, the finding is either deemed as a defect or a feature or taken further for a third opinion! In many cases, you might see that neither of the team members understands what a defect is and all the ways it can manifest.

Some defects are quite straightforward—the submit button does not redirect to the right page. This is a functional issue. But then you can have some uncommon defects, like an unintended filter getting applied on your reporting dashboard. Users might assume the unusual data combinations are a powerful, advanced filtering or reporting feature they didn’t know existed. But in reality, it is a defect that can lead to inaccurate reporting and derail decision-making.

Let’s understand defects better so that you can pick their scent from a mile away.

What’s the most common type of defect you’ve come across in your testing career, and how do you usually deal with it?

What is Defect in Software Testing?

A defect in software testing is basically a mistake or problem in the software that makes it behave in a way it wasn’t supposed to. It could be something like a button not working, the app crashing, or showing the wrong information. Think of it like a glitch in a video game where something doesn’t work as expected – that’s a defect in the software.

When testers find a defect, they report it so the development team can fix it. There’s an entire lifecycle process that the defect goes through. You can read more about it over here: Defect Lifecycle.

Defect vs. Bug

The terms defect and bug are often used interchangeably, though they do vary slightly.

A bug is a problem or error in the software/code that causes it to behave unexpectedly or incorrectly. It’s a term that’s more commonly used in day-to-day conversations. For example, if you click a button and nothing happens, that’s a bug. Read more about bugs over here: 7 Most Common Engineering Bugs and How to Avoid Them.

A defect is a broader term. It refers to anything that doesn’t meet the software’s requirements or expected behavior, including bugs. So, a defect could be a bug, but it could also be a mismatch between what the software was supposed to do and what it actually does. For example, if the software was supposed to show a message when a user clicks a button, but it doesn’t, that’s a defect.

Types of Defects

How do you prioritize defects from different categories when you're tight on time—do some types always take priority over others?

Here are the common types of defects.

Functional Defect

When the software doesn’t do what it’s supposed to, we see a functional defect. The functionality or behavior doesn’t match what the requirements say.

• Example: A shopping website has a “checkout” button, but when you click it, nothing happens. The button is supposed to take you to the payment page, but it doesn’t work.
• Why it matters: If the software can’t perform its core functions, it can’t serve its purpose.

Performance Defect

They are related to how well the software performs. If the software is slow, crashes, or takes too long to respond, it has a performance defect.

• Example: An app takes 10 seconds to load a simple page, which should only take a few seconds.
• Why it matters: Slow performance or crashes frustrate users and can lead them to stop using the software.

Usability Defect

When the software is hard to use, understand, or navigate. It’s about the user experience.

• Example: A mobile app has buttons that are too small to click or a menu that’s hard to find.
• Why it matters: If the software is confusing or uncomfortable to use, people won’t want to keep using it.

Security Defect

When the software has weaknesses that could be exploited by hackers or unauthorized users.

• Example: A password field in a website doesn’t properly hide the entered password or an app stores sensitive information in an unsecured way.
• Why it matters: Security defects put user data and the software at risk of being attacked or stolen.

Compatibility Defect

These defects occur when the software doesn’t work properly on different devices, browsers, or operating systems.

• Example: A website looks fine on Google Chrome but doesn’t display correctly on Firefox or Internet Explorer.
• Why it matters: If software doesn’t work well across multiple platforms, users might face issues depending on what device or browser they use.

Interface Defect

These defects are related to the way the software interacts with other systems or components.

• Example: The software fails to connect to a database, or it gets the wrong data from another system.
• Why it matters: If systems can’t communicate correctly, it can cause incorrect behavior or prevent the software from working at all.

Syntax Defect

They occur when there’s an error in the code itself. It’s like a typo or mistake in the programming language that prevents the code from running.

• Example: Missing a semicolon or using the wrong variable name in the code.
• Why it matters: Syntax errors prevent the software from working correctly or at all.

Arithmetic Defect

They happen when there’s a mistake in the mathematical operations or calculations performed by the software.

• Example: An online shopping cart adds up the total cost of items incorrectly, like adding 2 + 2 as 5 instead of 4.
• Why it matters: If arithmetic defects are present, the software may give users the wrong results, like charging the wrong amount, which can lead to frustration or loss of trust.

Logical Defect

These defects occur when the software doesn’t follow the correct logic or reasoning. This happens when the program runs but produces incorrect results due to a flaw in the decision-making process in the code.

• Example: A weather app shows that it’s sunny when the code says, “if it’s rainy, display sunny” because the logic is reversed.
• Why it matters: Logical defects lead to the software working incorrectly, even if no errors are visible. It can make the software give wrong information or fail to perform tasks as expected.

Multithreading Defect

They occur in programs that perform multiple tasks at once (in different threads). These defects happen when these tasks are not properly managed, leading to issues like race conditions or deadlocks.

• Example: A social media app shows an outdated notification because one task is still running in the background while another task is trying to update it. This can cause conflicts in data handling when multiple threads access the same resource.
• Why it matters: Multithreading defects can cause unpredictable behavior, crashes, or slow performance because different parts of the program may be working at the same time in conflicting ways.

How to Categorize Defects

Let’s talk about identifying defects. The above mentioned types of defects give a fair idea of where you need to look for.

Do you have a favorite tool or technique for identifying certain types of defects faster? Share your go-to methods!

Here’s a quick path to identifying defects:

• Test the Software: First, run the software and use it as a user would. Perform actions like clicking buttons, entering data, or opening pages to see if everything works as it should. Cover aspects such as functionality and non-functional requirements like performance, security, and usability.
• Compare Expected vs. Actual Results: Testers know what the software is supposed to do (expected results). If the software behaves differently or doesn’t work as expected, that’s a defect. For example, if you enter an email and click “Submit” and nothing happens, that’s a defect.
• Use Testing Tools: There are tools that help testers find defects automatically. These tools check the code and behavior of the software to identify any issues.
• Get Feedback: Sometimes, users or developers notice issues, and testers can find defects based on this feedback. For example, if users report that a button doesn’t work on a certain device, that’s a defect that needs to be checked.

Once a defect is found, it’s important to categorize it to prioritize fixing it. Categorization helps developers know what type of problem they’re dealing with so they can fix it efficiently. Consider the following ways to categorize defects:

• Based on Nature: These are the types of defects discussed above like functional defects, syntax defects, etc.
• Based on Sensitivity: Severity and priority guide how defects are managed, from fixing urgent issues to addressing smaller problems later. Read more about defect management: Mastering Defect Management: Understanding Severity vs. Priority in the Life Cycle.

What is Defect Clustering and Defect Cascading

Defect clustering is where a majority of defects are present in a small number of modules or components of a system (i.e., clustered). This follows the Pareto Principle (80/20 rule). Which says that 80% of defects are often found in 20% of the application areas. This exists due to complexity, frequent code changes, or legacy dependencies.

On the other hand, defect cascading occurs when an undetected defect in one module initiates a chain reaction of failures in other dependent modules. These issues travel across the system and cause multiple failures. Thus, it results in increased debugging complexity. Cascading defects are particularly common in highly integrated systems. The reason is that a small issue in an upstream component can cause issues in the downstream modules.

So, in short:

• Defect Clustering helps focus testing where defects are most likely to occur.
• Defect Cascading highlights the risk of system-wide failures due to undetected defects.

Best Practices for Managing and Preventing Defects

• Start Testing Early: The earlier you find a defect, the easier and cheaper it is to fix. You can run tests on small parts of the software as they are developed rather than waiting for the whole thing to be finished.
• Write Clear Requirements: Defects often arise when the software doesn’t meet what was actually needed or expected. Make sure the goals, features, and functionality of the software are clearly documented and understood by everyone (developers, testers, product managers). Consider non-functional specifications, too.
• Use Automated Testing: With automated testing you can run the same tests over and over without human intervention. Set up automated tests for repetitive or critical tasks, like checking whether buttons work or forms submit correctly.
• Have Code Reviews: Sometimes, defects come from simple mistakes in the code that could have been easily spotted. Have developers review each other’s code before it’s finalized. Look for potential mistakes, improvements, or areas where the software might not work as expected.
• Assign Defect Priority: Not all defects are equally important. Some defects can break the software, while others might be cosmetic issues. Classify defects by their severity (how serious they are) and priority (how urgent they are to fix). For example, we should fix a bug that crashes the app before a minor typo in the text.
• Regression Testing: Every time a new update or feature is added, we run tests on the parts of the software to identify new defects that might have been introduced.
• Stable Test Environment: If the testing environment (the system where tests are run) is not stable or different from the actual user environment, it can lead to inaccurate results. Make sure that the software being tested is in the same setup as users would experience it, whether that’s on different devices, browsers, or operating systems.
• Learn from Past Defects: Looking at previous defects can help prevent the same mistakes from happening again. Keep track of common defects that occur regularly. Use this information to refine coding practices, testing approaches, and training for developers and testers.
• Use Continuous Integration: Continuous integration (CI) involves regularly merging code changes into the main software project. Set up CI tools that automatically test and integrate new code frequently (e.g., every time a developer commits a change). This helps catch defects before they pile up and become harder to fix.

Automated Testing to Prevent Defects

You can prevent defects a lot better if you employ automated testing. Opt for tools that eliminate the need for you to worry about complex test creation processes and spend a lot of time in test maintenance. Of the many tools available in the market, testRigor is one that outshines due to its numerous features.

This generative AI-powered tool makes sure that you are easily able to create good test cases. Here’s how this tool helps with effective defect prevention:

• Easy Test Creation: This tool provides easy ways to create test cases. You can either write tests using plain English statements or use testRigor’s generative AI feature to create tests for you. Thus, everyone in the team can participate in the QA activity. Read more on different ways to create test cases in testRigor: All-Inclusive Guide to Test Case Creation in testRigor
• Automate All Kinds of Scenarios: testRigor lets you write tests in simple English language. This means that you no longer need to worry about programming languages to build test automation. Automate regression, UI, functional, end-to-end, and even API tests without dependence on application code.
• Negligible Test Maintenance: If you end up spending most of your time maintaining and fixing older test cases, then how are you going to focus on defect prevention? Luckily, testRigor uses AI to take this burden off you. Read more: Decrease Test Maintenance Time by 99.5% with testRigor
• Easy Integrations: You can integrate testRigor with your existing CI/CD or test case management systems to make sure that all your test cases are being run as desired.

This cloud-based tool lets you test across multiple platforms and browsers efficiently. There’s a lot more you can do with testRigor. Take a look at the tool’s offerings over here – testRigor’s features.

Conclusion

While defects might seem daunting, you must remember that they can teach you a lot about the software. For example, areas that need more attention. It’s a lesson not just for testers but also for developers, as uncovering defects presents an opportunity to do things differently – test differently, write code in a different way, or change aspects of the existing software. By understanding the different types of defects, you can further learn the aspects of the software that are prone to be vulnerable.

Additional Resources

• The Strategy to Handle Defects in the Agile Development Methodology
• Masked Defects Uncovered: Shining Light on the Hidden Flaws
• Defect Triage in Software Testing
• Latent Defects Decoded: The Hidden Perils in QA
• When to Stop Testing: How Much Testing is Enough?

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Source: https://testrigor.com/blog/types-of-defects-in-software-testing/?utm_source=LinkedInPosts

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