What is a Bug in Software Testing? Demystifying Software Errors

June 18, 2024

Curious what is a bug in software testing? Discover its impact on software performance & learn effective strategies to identify, fix, and prevent them!

Curious what is a bug in software testing? Discover its impact on software performance & learn effective strategies to identify, fix, and prevent them!

In software testing, a bug refers to a wide range of issues and problems with software. These problems can cause the software to stop working as it was intended. Software bugs can cover a wide variety of types and degrees of seriousness. 

Small bugs can involve minor problems with functionality and the UI, while major bugs can cause the software to break or crash. Software testing aims to find and fix bugs by putting the software through its paces. Bugs are also often called defects. Understanding what are bugs in software testing helps prioritize and address them effectively.

Importance of Understanding Bugs in Software Testing

What is bug in testing? During software development, certain errors or defects can be introduced to the code that causes things to malfunction. These are called bugs and cause unexpected results, ranging from UI elements rendering incorrectly to full crashes. As an integral part of software testing, bugs must be identified, tracked, and fixed to ensure the software becomes release-ready and functions as intended when it reaches the end user.

Bugs can go beyond breaking the software's functionality at the points of their existence. One bug can cause a ripple effect in separate areas of the software. Errors further down the execution chain can, therefore, sometimes be fixed by sorting out a bug that came much earlier. This is something to remember during bug fixing, where anticipation must be employed to understand the possible effects of specific bugs further down the execution chain.

Bugs are usually classified according to their severity and impact on the development and testing process. Here is a template of bug severity based on impact.

  • Low - A cosmetic defect with minimal impact. An immediate workaround can be applied in isolation, and the rest of the process can continue as usual.
  • Medium - A defect with localized impact but can be sorted with a workaround. One or a few testing streams might need to be stopped and restarted after the fix, but the rest commences as usual.
  • High – A major defect that severely impacts the functionality and features of the software. This usually requires one or more software features to be disabled during testing. An immediate fix is usually the best solution as workarounds can give rise to more problems down the line.
  • Severe—This usually causes the entire software to stop working meaningfully. There are no workarounds, and the software is unusable until the bug is properly fixed and retested.

What Causes Bugs in Software?

During the software development life cycle, quite a few events might result in a bug of some kind. More often than not, they happen due to certain common causes. Here are a few.

  • Most often, bugs are caused by errors in the programming or code. This can be due to human error or a lack of consistency in the coding standards for different parts of the software. Bugs can be resolved to a significant degree through thorough code review and then through unit testing.
  • A lack of time can often lead to the creation of bugs. Projects involving rushed and strict deadlines can sometimes lead to hastened coding, a scenario ripe for bugs.
  • Sometimes, bugs are caused by ambiguities in the requirements. When requirements are unclear across the development team, bugs can be introduced. Detailed reviews and static testing techniques can be employed to avoid this.
  • Bugs can happen due to human errors. These can include mistakes in coding, logic errors, or simply overlooking things. Even experienced programmers make mistakes, so avoiding errors completely is impossible.
  • Software must be capable of operating across different environments. Differences in these environments, such as operating systems, hardware configurations, and network setups, can lead to compatibility problems and unexpected bugs in the software. 
  • Modern software consists of various components. As these software solutions grow in complexity, they become increasingly challenging to develop and maintain smoothly. The more intricate the software becomes, the higher the likelihood of introducing errors or bugs during development. 
  • Effective communication and strong relationships among team members are essential in any project. Miscommunication or ineffective collaboration can cause discrepancies between the desired requirements and the actual solution that is implemented, which often leads to bugs in the software.

Types of Bugs in Software Testing

Different types of bugs might appear during software development and each of them has a different classification. Here is the list of the most typical bugs in software testing:

  • Functional Bugs: These bugs are issues in software that cause a problem with how it's supposed to work. They might cause wrong calculations, make it act strangely, crash, or stop features from working. 
  • Unit Level Bugs are errors found in the smallest parts of a software system. Developers divide their code into these units to manage and test it more effectively. This method helps catch and fix issues early.
  • Performance Bugs are an issue that negatively impacts software stability, how fast it runs, or how quickly it responds to user inputs. They slow down the system or make it unresponsive.
  • Usability Bugs are errors that occur during the design of the user interface, making it ineffective. This means the interface prevents users from performing their tasks easily or efficiently. As a result, they may find it difficult or time-consuming to accomplish what need to do.
  • Security bugs are ongoing and serious problems in the tech world. These bugs can be exploited to gain unauthorized access or privileges on a computer system. Attackers can steal sensitive data or cause other damaging effects. 
  • Logical bugs disrupt software's intended workflow and cause it to behave incorrectly. These bugs can lead to unexpected software behavior and even sudden crashes. They primarily occur due to poorly written code or misinterpretation of business logic.
  • Compatibility Bugs occur when software is incompatible with the hardware or cannot be processed by the operating system. Such bugs arise when the software fails to run correctly on different devices, operating systems, or environments.
  • Syntax Errors are very common and typically happen when there are missing or incorrect characters in the code. These occur in the source code of a program 

How Bugs Impact Software Development 

Bags have a significant impact on the software development process and user experience. Here is a list of a few impacts that are caused by them: 

  • Delayed Project Timelines: Debugging and fixing bugs can take a lot of time. This may delay the development schedule, causing missed deadlines and projects exceeding budget.
  • Increased Costs: The cost of identifying and correcting defects in software grows significantly as time goes on in the software development process. Fixing bugs discovered after the software has been released can be extremely expensive and risky.
  • User Dissatisfaction: Software bugs cause confusion, frustration, and dissatisfaction. They interrupt development and negatively affect users.
  • Reputational Damage: Frequent bugs can harm a software company's reputation and reduce user trust in the product. 

How to Find and Solve Bugs?

Every bug that is found goes through a complete life cycle till it is closed. During testing, a number of techniques can be deployed to find and understand bugs. Here are a few steps that can help.

  • First, it’s critical to develop a thorough understanding of the software or software modules that you are testing. This improves the chance of finding bugs.
  • To start off, you need exhaustive high-quality test cases and test data. Focus on functional test cases which target the potential vulnerabilities or breaking points of the software. Also, thorough test data that covers the test conditions can be crucial.
  • For best results, tests can be repeated inside different test environments for consistent results.
  • Use the right testing and bug tracking platform. A resource such as Functionize Architect, with its Ai-driven framework and seamless integrations, can really speed up your workflow.
  • It’s a salient idea to go ahead with some standard test cases. These are targeted towards known vulnerabilities and can help you eliminate possibilities.
  • Finally, it’s crucial to keep a mindset that encourages breaking the application. Going down this path, even subtle bugs can come to the front.

The bug life cycle usually involves bugs being classified as “new” when found and “open” when accepted by the development team. They are then labeled “fixed” when the developers sort out the bug and “closed” when it passes subsequent testing.

The Bug Lifecycle 

The bug life cycle contains different phases that a bug goes through, from detection to fixing.

  • Bug Detection is the process of identifying errors or issues within software programs.
  • Bug Reporting is the process of documenting the details of a bug, such as how it was found, its effects, and other relevant information.
  • Bug Tracking follows, where the bug is assigned to a developer or team responsible for fixing it.
  • Bug Fixing is the process of resolving the identified issue within the software code. 
  • Bug Verification occurs to ensure that the fix implemented has effectively resolved the bug and that the software now functions correctly. 

Best Practices for Bug Management

Regular Testing

Regular testing should be conducted to identify bugs early in the development process. When the code is frequently tested, issues can be caught before they become more complex and costly. Incorporate the following into your regular testing routine:

  • Unit Testing: Finding problems early, preventing impact on other components. It encourages building resilient code.
  • Integration Testing: Verifying that different components work together as expected.
  • System Testing: Testing complete and integrated software to ensure it meets the required standards.

Automated Testing

Automated testing enhances the bug management by providing consistent and repeatable tests without human intervention. These tests can be run frequently and quickly, catching bugs that might be missed in manual testing. 

Code Reviews

Having multiple developers review code before it is merged helps in identifying potential issues. Key benefits of code reviews include:

  • Early Detection of Bugs: Reviewers can spot mistakes that the original developer might have missed.
  • Knowledge Sharing: Code reviews facilitate knowledge transfer among team members.

Clear Documentation

Proper documentation can ensure that all team members have a shared understanding of the system. Important documentation practices include:

  • Commenting Code: Providing clear comments within code explains complex logic and decisions.
  • Maintaining Logs: Maintain detailed logs of all changes and updates to the codebase.
  • User Documentation: Documenting how to use the software helps in identifying user-reported bugs.

FAQs on Bugs in Software Testing

What is the most common type of bug in software testing?

The most common type of bug in software testing is coding errors. These are mistakes in the code that make the software run. Coding errors can cause systems to crash, produce unexpected errors, or give incorrect output.

What is the difference between a bug and a defect?

A bug is a specific error in the code that causes incorrect or unexpected behavior. A defect is a broader issue that includes bugs and other deviations from requirements or specifications.

Why do bugs reappear after being fixed?

Bugs can reappear after being fixed due to several reasons:

  • Incomplete Fix: The initial fix might not have addressed the root cause of the bug, only its symptoms.
  • Code Regression: New changes or updates in the code can reintroduce the same bug.
  • Insufficient Testing: There are many conditions under which the bug fix might not have been thoroughly tested.
  • Dependencies: Changes in external dependencies or third-party libraries can cause a previously fixed bug to resurface.
  • Human Error: Developers might accidentally reintroduce the same bug or a similar one due to misunderstandings or mistakes during the coding process.

How does continuous integration (CI) help in preventing bugs?

CI prevents bugs from spreading in the codebase by running automated tests frequently. It encourages developers to fix issues quickly before they become more complex.


  • Bug testing helps identify and resolve issues before they become more complex.
  • Knowing what is bug in software testing makes it easier to understand, identify, and deal with them through rigorous testing.
  • Bugs can be tricky to identify with automated tests due to frequent breaks and false positives.
  • Functionize helps find and fix bugs faster with easy-to-understand test results, step-by-step screenshots, and troubleshooting logs.
  • Test results can be quickly shared with colleagues via link, exported, or emailed reports.
  • The Functionize Jira integration helps you stay on top of developers' progress by filtering and running tests as soon as bugs are ready for verification.

About the author

author photo: Tamas Cser

Tamas Cser


Tamas Cser is the founder, CTO, and Chief Evangelist at Functionize, the leading provider of AI-powered test automation. With over 15 years in the software industry, he launched Functionize after experiencing the painstaking bottlenecks with software testing at his previous consulting company. Tamas is a former child violin prodigy turned AI-powered software testing guru. He grew up under a communist regime in Hungary, and after studying the violin at the University for Music and Performing Arts in Vienna, toured the world playing violin. He was bitten by the tech bug and decided to shift his talents to coding, eventually starting a consulting company before Functionize. Tamas and his family live in the San Francisco Bay Area.

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