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Home Guide Bug vs Defect: Core Differences

Bug vs Defect: Core Differences

By Kalpalatha Devi, Community Contributor -

Bugs, Errors, Defects are all used interchangeably in testing. This guide explains in detail the difference between a bug and a defect.

What is a Bug?

In the Software development life cycle, the project team gathers customers’ requirements, analyzes them, designs the UI, and develops and tests the required software.

The SDLC  model decides when testing is to be carried out on the developed software. For example, in the Waterfall model, testing is done after the complete development of the software, whereas in the V-model continuous testing is carried out at each stage of SDLC, and when it comes to Agile, testing is done for all the users stories. No matter which SDLC model is used, testing is a must, and whenever a tester observes an unexpected behavior of the software in testing, they will report it as a bug. 

A bug alters the behavior of the software and the software does not function as expected. Bugs can be functional, behavioral, or cosmetic. Any deviation from the user story, any glitch in the UI, or if the software does not function as intended by the developer then it is termed a bug.

A bug can cause malfunction. A bug could occur due to multiple reasons like coding errors, inadequate understanding of the requirement,  miscommunication between teams, misunderstanding the requirements and designs, the complexity of code, design, architecture, and changes in the environment, etc. They are generally found during the testing phase. For example, assume you have asked the user to select three options in a form, but instead of a checkbox, there is a radio button.

Examples of different bugs

  1. Functional bug: the user cannot log in to a website, or the search option is not working, and a high-priority bug is the application crashes or hangs
  2. Cosmetic bugs:  Screen alignments, section divisions, string truncations, translation issues, the color of the texts, etc.
  3. Performance bugs:  When the application takes a long time to load a screen, and the screen navigation in the application is very slow, etc. 
  4. Compatibility bugs: When software behavior is inconsistent among different  operating systems and multiple browsers.

How To Track and Rectify a Bug

Bug tracking is essential in the testing phase; the tracking process varies from project to project, even in the same organization. There are so many bug-tracking tools – some are open source, whereas some are proprietary tools. Bug tracking includes documenting, categorizing, assigning, reproducing, correcting, and retesting from identification to the closure of the bug. These tools are useful for tracking and are easy to convey among different teams. The QA team will report the bugs through the bug tracking tool, and the development team will validate and rectify the bugs. Then the QA team will retest and confirm the closure of the bugs.

Bug tracking with proper documentation helps to understand the bug; there should be details of the function area, steps to reproduce, screenshots, a tester who has  identified the issue, and details of the developer who is responsible for fixing it, etc. 

Most of the time, testers face an issue with reproducing the bug, this could majorly be because, the bug could only appear in selected browsers, browser versions or devices. What might appear as a bug in Chrome Version 108.0 might not be a bug in Chrome Version 107.1. Therefore it is essential to understand the environment and the setup in which the bug was identified inorder to rectify it.


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Accurate debugging and unit testing helps to reduce the issues from the developer ned itself. Once an issue is identified, it will be rectified by reproducing the issue and analyzing the logs, and correcting and testing. The code will be released to the testing team for the retest.  

Best Practices in Bug Tracking and Management

Bug tracking is an essential phase in the test execution phase, proper tracking and management impact the team efforts.

  1. Prevention is better than cure; defect prevention can save time and energy for the team, so during the development phase itself, if the team is much more clear on requirements and technology reduces the possibility of bugs. 
  2. Introducing early testing in SDLC can also reduce minor and major issues in later stages. Baseline documents or functional document reviews can be carried out at the early stage; identifying risks and estimating the impact, and originating the bugs also can be easy.
  3. Choosing the right tracking tools makes the job easy for the team; the tools should be simple and easy to use by both DEV and QA teams. 
  4. Once the issues are identified, bug information should be provided clearly, like the steps to reproduce, description of the issue, functional area, and proper proof of bugs like screenshots and recordings need to be clear and simple to understand the issue by anyone.
  5. Communication between the teams should be clear and should not lead to any confusion it should be healthy and understanding, aiming for the quality of the software.
  6. Prioritize issues for any reported bug, severity, and priority are required to mark accordingly to focus on high-priority and impacted issues to close first.

What is a Defect?

A defect is also the unexpected behavior of the software but observed after releasing the software to the user means in production. If the feature does not work as per the user’s requirements, then it is termed a defect. A defect affects the usability and experience of the software. 

Defects can occur due to poor design, requirement mismatch, incorrect data, or unexpected errors. Defects are hard to fix when compared to bugs. The cost of fixing a defect is also higher. Sometimes, it becomes difficult to fix the defect due to the massive code change that it comes with; in such cases, the users might have to use the software with the defect and find a workaround to solve the problem. For example, the user cannot add more than three products to the cart. 

Example of Defects

  1. Design defects: Assume the logo of a company is improperly displayed on the home screen of any application. It is a major issue that needs to be fixed immediately as it will impact the company’s reputation.
  2. Logical defects: Code errors and issues due to incorrect logic in code, these types of defects can occur due to misunderstanding of the requirement. Assume there is a file upload option on the website if it fails to upload after a certain file size.  (Assume the file size limit is 100 MB, but the software is failing to upload a 10 MB file).
  3. Integration Defects:  When multiple modules exist in any software development, modules should interact with each other in such cases; integration testing will be carried out if any issues are missed out, capture at this stage may lead to a defect in production.  ( Assume a mail trigger option fails to send mail to respective users). 
  4. Performance Defects: The performance of any software is down in certain conditions. Assuming there is a delay in alerting the user of unauthorized access to his account, there will be a huge loss.

How to Track and Rectify Defects

Defect tracking is crucial for any software development; usually, any software before moving to the market will release a Beta version of the software to specific users to get feedback on any issues observed during this phase can be tracked using the defect tracking tools and can be rectified by the developers. The defect tracking tools are very useful in the beta cycle as these will provide clear information to the developer for fixing the issue. Sometimes defects can occur even in the production environment; these are also tracked using the tracking tools.

Once the issue is identified in production, there will be an incident logged against the issue, and the problem description is provided with that, and the release team will track this; a change request will be created for the development, and then developers will try to reproduce the same in dev environments and do a root cause analysis of the defect. Once the issue is fixed and it will be tested in the test environment, and regression testing will also be performed to ensure the code changes are not impacting any new issues, and then it will be sent to release for production as a CR. A patch release will be done on the software with new changes.

Best Practices in Defect management 

Defect management is an important phase in the test execution, So for a better process in place, one should take care of defect-tracking.

  1. Thorough analysis of the requirements reduce the possibility of defects.
  2. Code reviews and risk analysis need to be performed. 
  3. Performing a defect analysis to reduce the reoccurrences of the defects and reduce the rework and also improves the communications among teams.
  4. Describing the defect with complete details like steps to reproduce the issue, functional area where is happening, and describing the actual output and expected output.
  5. Assigning the priority and severity of the defect.
  6. Proper planning of test strategy decreases the possibility of defect leakage. 

Difference between a Defect and a Bug

Bug Defect 
When there is a code error, requirements are not implemented correctly, and resulting unexpected behavior leads to a bug.When requirements are implemented in the wrong way, and resulting a deviation in customer specifications which leads to a defect.
A bug is an error in the software that causes malfunction. A flaw in the product that reduces its usability of the product.
Observed during unit testing by the developer or during system testing done by the tester.Observed by customers once it is available to customers.
Identified in a test environment or dev environment,  easy to track and fix.Identified in the production environment by the customer, so tracking and fixing are tough.
Changes and corrections can take less  time and cost.Changes and corrections are time taking and costly.

Bug or defect is a term used interchangeably by most people and depends from project to project and organization to organization. But if the issue identified in the development environment means before moving the software to production is called a bug. Once the software is in production, any issue identified by the end users is called a defect stating it as defective software. 

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