Current Date :July 21, 2024

Why do software bugs occur? Types of Defects in Software Testing

Do you know what defects are in software testing? Yes, those that negatively affect the performance of software and bug users.

There are many types of bugs in software testing that occur during the development process. This article aims to define a bug in software testing, describe the most common types of software bugs, and explain why bug testing is important for software development. It’s going to be insightful.

What are software bugs? 

In software testing, it is impossible not to find bugs. You know, people make mistakes when they create software. Moreover, customers may misuse your solution, for example, by entering invalid data. Due to this, all your users will discover your software’s bugs. 

So what are these software defects? 

A software defect (a bug) is an error in a program that causes it to work inaccurately and (or) unpredictably. A software defect definition also contains the difference between the actual and expected result. 

As bugs in software are created while writing the code, your software may not execute the pre-planned features, work in a manner that differs from your specifications, or perform actions that it shouldn’t. Such cases are called program failures.

Every software has either these or those kinds of software bugs. Moreover, bugs often remain there even after the official release. This is because catching all bugs in the software testing process is nearly impossible. Application bugs might occur due to the lack of time, and resources, or simply wrong input values and an arrow in validation scripts.

A released software usually comes with minor errors. Major and critical errors come fixed.

Types of software Errors

Each of the software development departments has its bug classifications. However, in our article, we’ve concentrated on the most widespread and most typical bugs discovered in software and app.


We think this is the most serious kind of software bug. A program (written in any language) runs perfectly but produces the wrong output. The flaw here is in the underlying programming logic. These kinds of defects are inherited from a defect in the underlying algorithm. The logic on which the complete software is based is flawed.

Finding a solution to this error needs a fundamental change in the software algorithm. 


Computer languages such as C, Java, Perl, or Python have detailed syntax. Every time a developer fails to adhere to the “grammar” of the computer language specifications, a syntax error will appear.

These software bug types are easily destroyed at the compilation stage.



Compilation is the method of converting a program written in a high-level language into a machine-readable form. Many kinds of bugs can happen at this stage, including syntax errors. Even in the case when the syntax of your application source code is perfect, a compilation error can still happen. This often can be due to a problem in the compiler itself.

These software bugs are fixed at the development stage.


The program code was compiled successfully and the executable file was built. You breathe a sigh of relief and run your software to see how it performs. Errors during software usage can happen as a result of a crash or a lack of media resources. Your dedicated team of developers requires to anticipate the actual deployment requirements of your software.

These types of software defects can be resolved by going back to the coding stage and refining it all there.


Resource errors occur when the value of a variable overflows the maximum permitted value. Such bug examples contain:

– Buffer overflows;

– Use of an uninitialized variable;

– Access violations;

– Stack overflows.


These types of software errors arise due to a software-hardware mismatch, a mismatch with your application interface. If we’re talking about web applications, an interface error can come as an outcome of the misuse of the web protocol.

What causes software bugs: main causes for software defects

You surely understand that just overviewing the bug categories is not enough to ensure your software from software defects. Apart from understanding the bug definition in software testing, it’s also necessary to realize the root causes for bugs to appear.

Normally, software bugs happen the moment the three following requirements are met simultaneously:

  • The expected outcome is known;
  • The actual outcome is known;
  • The actual outcome is different from the expected result.

However, not all bugs cause software failures. Some of them may not manifest themselves in any method and remain unseen(or as it often happens appear only under very specific circumstances).

Software operation failures can be caused not only by errors but also by environmental requirements such as radiation, electromagnetic fields, or pollution. They can impact the operation of both software and hardware.

Root causes of software defects and failures contain:

  • Errors in the specification, design, or execution of the software system;
  • System usage bugs;
  • Adverse environmental conditions;
  • Deliberate harm;
  • The potential consequences of previous bugs, conditions, or intentions. 

Bugs can happen at various levels of a QA process flow. Your software quality will directly depend on whether these defects are corrected and at which stage.

5 reasons for software defects

Summing up all the types of defects in software testing and keeping in mind the software bug classification, we have outlined 5 main reasons for software defects:

Lack of team communication

There are times when business requirements do not reach the development team. Clients understand how they want the finished product to work. Your dedicated development team and QA specialists may not be able to understand your idea if it is not properly explained to them.

During software development, all stakeholders should be able to access and understand requirements.

The complexity of your software

Modern software consists of components that are combined into complex software systems. Multithreaded applications, client-server, distributed architecture, multi-tier databases… Software solutions are becoming more difficult to build and maintain.

The more complex the work on your software is, the more mistakes your software might contain.

Updates to the requirements 

Even minor changes to the requirements at a later stage of development require a lot of work within the already-built system. At the moment when the design and architecture of your application change, changes come to the source code and the underlying principles of interaction of the software modules. 

Ongoing changes are often the source of subtle defects. Frequently changing requirements in modern business has become more of a rule than an exception.

That is the reason why continuous testing and DevOps of software and applications have become popular services in the IT field. DevOps help minimizes risks of low software quality.

Poorly documented code

It’s difficult to maintain and alter poorly written and poorly documented code. At large, software companies have rules for developers about writing and documenting the parts of code.

Although in practice it often occurs that developers are forced into writing software asap and this impacts the quality of the final product.

Also Read: Introduction To Integration Testing

Summing up

Software testing and debugging play an integral role in the software development cycle and can help nip these defects in the bud before they are released. 

It is possible to avoid mistakes by planning thoroughly during the coding phase. Through practice and rigorous debugging procedures, most bugs can be corrected during software development.

There will always be mistakes along the learning curve, and they can never be completely avoided. Our goal is to avoid repeating the same mistakes in the future. 

In case you need a team of talented QA specialists, contact TestUnity through the form on our website and our experts will help test your software solution no matter the development process phase.


Testunity is a SaaS-based technology platform driven by a vast community of testers & QAs spread around the world, powered by technology & testing experts to create the dedicated testing hub. Which is capable of providing almost all kind of testing services for almost all the platforms exists in software word.

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