Software testing is one of the most important parts of the Software Development Life Cycle (SDLC). The purpose of testing is not only to find issues but also to ensure the quality, reliability, and usability of a software product. While learning Manual Testing, you will frequently come across three very important terms: Error, Bug/Defect, and Failure.
Although these terms may sound similar, they have different meanings and are used in different contexts. If you want to become a good software tester, you must understand the difference between them.
In this blog, we will cover in detail:
- What is an Error in Software Testing?
- What is a Bug/Defect in Software Testing?
- What is a Failure in Software Testing?
- Difference between Error, Bug/Defect, and Failure.
- Real-world examples to understand the concepts.
- Importance of reporting bugs and failures properly.
- How testers can prevent errors and failures in software.
What is an Error in Software Testing?
An Error is a mistake made by a software developer or programmer while writing the code, designing the system, or creating requirements.
In simple words, an error is a human mistake. These mistakes can happen because of lack of knowledge, misunderstanding of requirements, wrong assumptions, or carelessness.
Definition:
An Error is a mistake or wrong decision made by a person while developing or designing software.
Example of Error:
- A developer writes
A = B + Cinstead ofA = B - C. - A requirements analyst misunderstands that the login should accept username only, while the client wanted username or email.
Errors may or may not be found during development. If not caught early, they can lead to defects in the softwa
What is a Bug/Defect in Software Testing?
When an error in the code, requirement, or design leads to an incorrect output or behavior in the software, it is called a Bug or Defect.
Definition:
A Defect (or Bug) is a deviation of the actual result from the expected result, observed during testing or after release.
Example of Bug/Defect:
- The login page allows incorrect password login.
- The mobile app crashes when the user uploads an image larger than 5MB.
- A banking application shows wrong account balance after money transfer.
In the industry, both words “Bug” and “Defect” are used interchangeably. Testers usually report these issues in tools like JIRA, Bugzilla, or HP ALM.
What is a Failure in Software Testing?
A Failure occurs when the software does not work as expected in real-time (production) environment, even though it was tested.
Definition:
Failure is the inability of a software system or component to perform its required functions within specified conditions.
Example of Failure:
- A website goes down during high traffic (e.g., online shopping sites crashing during sales).
- An ATM machine deducts money from the account but does not dispense cash.
- A flight booking application double-books a seat.
Failures usually impact end-users, which can lead to financial loss, customer dissatisfaction, or even safety risks in critical applications like healthcare and aviation.
Difference between Error, Bug/Defect and Failure
Here’s a clear comparison:
| Term | Meaning | Created By | Detected By | Example |
|---|---|---|---|---|
| Error | Human mistake in code, design, or requirement | Developer/Analyst | Developer/Tester (during reviews) | Misunderstood requirement |
| Bug/Defect | A deviation of actual output from expected output in the software | Error made by dev | Tester during testing | Login page accepts wrong password |
| Failure | Software not performing as expected in actual environment | Due to defect not fixed | End-User in production | Website crashes on high traffic |
Real-World Example
Let us understand with a real-world scenario:
- Error: A developer misunderstands requirement and codes discount as 15% instead of 50%.
- Bug/Defect: Tester finds that the system applies only 15% discount instead of expected 50%.
- Failure: If this defect is not fixed and goes live, customers will get less discount, leading to complaints and financial loss.
Why Understanding Error, Bug/Defect and Failure is Important?
- Helps testers in writing accurate defect reports.
- Improves communication between developers, testers, and business teams.
- Reduces misunderstandings during the SDLC.
- Enhances software quality and user satisfaction.
Role of a Tester in Handling Errors, Bugs, and Failures
- Identify Errors Early:
- Review requirements and designs carefully.
- Participate in walkthroughs and peer reviews.
- Report Defects Properly:
- Use defect tracking tools like JIRA or Bugzilla.
- Provide steps to reproduce, screenshots, and expected vs. actual results.
- Prevent Failures:
- Perform rigorous testing (Functional, Regression, Performance).
- Test under real-world scenarios and load conditions.
Best Practices for Testers
- Clear Communication: Always clarify doubtful requirements.
- Document Defects Well: A poorly written bug report may be ignored.
- Prioritize Testing: Test critical business flows first.
- Collaborate with Developers: Work together to fix errors before release.
- Continuous Learning: Stay updated with latest testing techniques.
Conclusion
To summarize:
- Error is a human mistake.
- Bug/Defect is when that mistake shows up in the software.
- Failure is when the software fails in real-world usage.
By understanding these differences, testers can improve the overall quality of the product and prevent costly failures in production.
Whether you are a beginner or an experienced tester, always remember: catching Errors early, reporting Defects properly, and preventing Failures is the key responsibility of a tester.