Balance between
quality and deadlines

What Is a Bug

Software is created by people, and people are prone to making mistakes. Therefore, errors in the code are inevitable, and one of the key tasks of testing is to detect and eliminate them. Such errors are called bugs.

bug dancing

Definition of a Bug

A bug is an error, defect, or unexpected behavior in a program that causes it to operate differently than expected. It can manifest as a crash, an incorrect result, or even a critical vulnerability.

Simply put, a bug is a discrepancy between the program’s actual behavior and its requirements or the users’ expectations.

Examples of bugs:

  • The Add to Cart button on a website doesn’t work.
  • A calculator that outputs 5 instead of 2 + 2 = 4.
  • An application crashes when attempting to open a file.
  • A password is displayed in plain text rather than being masked with symbols like ****.
  • A single click processes a payment twice.

Why Do Bugs Occur?

The reasons for bugs can vary, but the main ones include:

  • Human Factor - Developers, testers, and analysts can make mistakes.
  • Design Flaws - If the system is poorly designed from the start, errors are inevitable.
  • Code Complexity - The more complex a system is, the higher the probability of errors.
  • Unaccounted Scenarios - Testers and developers might not consider all possible use cases of the program.
  • Integration Issues - Interactions between different parts of the system or external services may not work correctly.
  • Data Errors - Incorrect input data can lead to failures.
  • Time and Resource Constraints - Sometimes bugs are overlooked due to rushed development.

Bug Classification

Bugs can be divided into several categories depending on their nature and impact on the system.

By Severity:

  • Blocker - Prevents further work with the program (for example, the application fails to launch).
  • Critical - Causes serious malfunctions or data loss (for example, a payment is processed but funds are not credited).
  • High - Affects the main functions of the application but does not render it completely unusable (for example, a website’s search function returns no results).
  • Medium - Causes inconvenience but does not hinder overall functionality (for example, a button is improperly placed).
  • Low - Cosmetic defects that do not affect functionality (for example, a typo in the text).

By Error Type:

  • Functional - The program does not perform its intended functions.
  • UI Bugs - Errors in the user interface (incorrect font, misaligned buttons, etc.).
  • Logical - Flaws in the algorithms (for example, an incorrect calculation of a product discount).
  • Performance - The program runs too slowly or cannot handle high loads.
  • Security - Vulnerabilities that may lead to data breaches or hacking.
  • Localization - Errors in translation or text display.

Bug or Feature?

Sometimes users perceive something as a bug even though it is intended behavior. For instance, if a messaging app does not allow the deletion of a sent message, it might not be an error - it could be a deliberate design choice made by the developers.

Therefore, before logging an issue as a bug, a tester should verify the requirements and ensure that the program’s behavior is indeed incorrect.

Bug Lifecycle

Each detected bug goes through several stages:

  • Detection - The tester discovers the error.
  • Reporting - The bug is recorded in a system (such as Jira).
  • Analysis - A developer investigates the cause of the error.
  • Fixing - The bug is corrected in the code.
  • Retesting - The tester verifies that the bug has been successfully fixed.
  • Closure - If the error no longer occurs, the bug is marked as closed.

Bugs are inevitable, but they can be minimized through effective testing. It is important not only to find errors but also to analyze their causes to prevent their recurrence in the future.