Causes of defects and failures

It is impossible to create software without mistakes. Software is created by people, and people tend to make mistakes. In addition, users may not use the program as expected and unintentionally enter invalid data, while the program also may not behave the way it should.

A defect (bug) is an error in a program which causes an incorrect and/or unpredictable operation; a defect is also a mismatch of the actual and expected result. Due to defects that occurred during code writing, a program may not perform its intended functions, work differently than required by the specification, or perform actions that are not expected. Such cases are called program failures.

All programs have bugs and they remain there even after release. It happens because it is impossible to conduct exhaustive testing. The reason is the lack of time, resources, and a huge number of input values and test scenarios. Usually, a software release contains minor bugs, while serious and critical bugs are fixed.

Defects can be found at different stages of development and can be detected at different levels of testing. The quality of the system depends on whether the bugs found are fixed, while the cost of fixing the bugs depends on the stage of software development at which the bugs are found.

Next, let's look at the most common reasons behind the error emergence.

1. Problems in communication between team members

Business requirements might not be conveyed to all participants in the development process or they might be conveyed in a distorted, incomplete, or contradictory manner, causing the requirements to be misinterpreted by development team members. Therefore, the requirements should be described in a clear, comprehensive, unambiguous manner and with no contradictions between different parts of the specification.

2. Software complexity

Software is made up of many components, and the components are combined into software systems. The requirements and software description contain a large amount of functionality of different complexity. Such software is difficult to develop and maintain, programmers make more mistakes, and, taking into account the complexity of the software being developed, the number of mistakes increases and becomes more serious.

3. Changing requirements

With the growing competition in software development, there is a need to make changes at different stages of development, and agile development models have emerged, creating new challenges and problems. Changes in requirements cause code changes, and the later it is decided to make a change in the requirements, the more work will have to be done implementing the changes to the system. Even if this change is minor, it can result in new defects or the return of already fixed defects.

4. Low-quality code documentation and time frames

Developers should write code following certain rules and document it, but in reality, it is not only important for them to create a high-quality product, but also to do it quickly. Usually, the lack of time forces programmers to write code quickly, leading to inattention and forgetfulness, which negatively affects the quality of the program.

5. Mistakes made by programmers

Thus, the human factor can be found in everything. Programmers also suffer from inattention, forgetfulness, accidental keystrokes, or lack of experience and skills. Meanwhile, a developer's positive attitude and level of programming skills are directly related to the quality of the code they write.

6. Bugs in software development tools

Software development tools also have bugs that can affect the quality of the product. These bugs can lead to both minor errors and those that block the developer's work. When a particular logic in a development tool is broken, it is obvious that the written code using it might also contain errors.

7. Mistakes made by testers

Testers' mistakes can be one of the reasons why bugs in the system remain after the release instead of being fixed initially. Testers might not notice errors due to lack of experience or they can miss problematic issues in the software due to its complexity and the impossibility to perform exhaustive testing.

8. Low-quality code version control

Program code versioning is a set of fixes within one program over a certain period of time. Versions are controlled during releases and updates of applications. There must be support for version compatibility, which means that new versions of the program can support old versions, and guarantee the execution of the program code written in the old version.

Poor version control can lead to a large number of bugs. This situation happens when versions do not match due to a lack of control over the programming language in which the application is written, the libraries used in the application, and also poor control over the module versions of the program. Newer versions might not support older versions and vice versa, and this is why errors occur.

9. Software architecture

Poorly considered choice of structural elements and system interfaces, their behavior in cooperation with other structural elements, connection of selected elements and the overall architecture of all elements lead to problems in the software functioning. Elements might not interact in the way the customer expects, be located in a place not expected by the user, and violate the business logic of the program.

10. Lack of funding

The software product is tested exactly as much as the funding for the testing process has been provided. The allocated budget may not be enough to test the system thoroughly and when the budget is exhausted, testing stops regardless of the test result.

In conclusion, the main causes of software bugs include the human factor, time and financial constraints, bugs in development tools, and the inability to conduct exhaustive testing, resulting in bugs being present in the software. Even if it may seem that there are no errors in the software, there are. Therefore, proper test planning, test prioritization, and bug fixing are important basics of high-quality software testing performed on time.