The lifecycle of a software bug begins with its introduction, which occurs when a defect is unintentionally created during any stage of the software development process, including requirements gathering, design, coding, configuration, system integration, or even deployment. Bugs may originate from various sources such as incomplete or ambiguous requirements, incorrect business logic, coding errors, environmental differences between development and production, external system failures, or overlooked edge cases. Often, defects are injected due to tight deadlines, poor communication between stakeholders, or a lack of sufficient peer reviews. At this point, the bug is present within the system, but it remains undetected by both the team and the end users.
The next stage is detection, wherein the defect becomes visible through testing or operational use. Bugs can be discovered during different layers of validation such as unit testing (performed by developers on individual components), integration testing (focusing on the interaction between modules), system testing (validating the end-to-end flow), or acceptance testing (ensuring the system meets user requirements). Bugs may also surface after release, often reported by customers or internal support teams. Detection is not always immediate; some defects may remain dormant for months if they reside in rarely used features or if triggered only under specific, complex conditions. Early detection is preferable, as the cost of fixing defects escalates dramatically the later they are discovered in the lifecycle.
Once a defect is detected, the process moves into the bug reporting phase. It is critical at this stage to capture as much contextual information as possible to enable efficient diagnosis and correction. A comprehensive bug report includes a unique identifier, a summary and detailed description, reproduction steps that reliably trigger the issue, observed versus expected results, screenshots, error logs, stack traces, information about the test environment (such as browser versions, device types, server configurations), and a categorization of the bug's severity and priority. Severity reflects the impact on system functionality (for example, data loss is severe, cosmetic misalignment is minor), while priority dictates the urgency of resolution from a business perspective. In organizations practicing Agile, teams often define “Definition of Ready” criteria for bug reports to ensure high-quality entries.
Following reporting, the defect enters the triage phase. During triage, a cross-functional team — typically comprising the product owner, QA leads, development leads, support representatives, and occasionally business analysts — reviews incoming defects to confirm their validity and assess their importance. Triaged defects are classified based on severity (blocker, critical, major, minor, or trivial), assigned business impact, frequency of occurrence, and affected user segments. Decisions made during triage may include accepting the defect for immediate fixing, deferring it to a future sprint or release, merging it with existing defects if it’s a duplicate, reassigning it if it's misfiled, or rejecting it altogether if found to be invalid or working as intended. Triage also often considers risk analysis: for example, whether the fix might destabilize critical paths in the system.
Once triaged and confirmed, the bug moves into the assignment phase. It is allocated to a specific developer or team based on expertise, availability, and ownership of the affected module. During the bug fixing stage, the developer analyzes the defect by reviewing the codebase, reproducing the issue in a controlled environment, examining related documentation, and conducting root cause analysis (RCA). Fixing a defect may involve code correction, database updates, configuration adjustments, updating third-party libraries, or modifying integration points. Developers typically create new unit tests or adjust existing ones to capture the corrected behavior and prevent regressions. Before considering the defect fixed, developers perform local validation to ensure that the change solves the problem without introducing new issues.
The defect then advances to the verification stage, where the QA team re-executes the originally reported steps in a clean, controlled environment. Verification ensures that the issue has been effectively resolved, that the system behaves according to the expected outcome, and that no unintended side effects have been introduced elsewhere — a process known as regression testing. In more mature environments, automated regression suites, smoke tests, exploratory testing, and performance validation may be employed alongside manual validation to ensure comprehensive coverage. If the fix passes verification, the bug is moved to a closed status, and closure is documented with appropriate comments and evidence of successful validation.
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