Defect Fixing Phase in STLC: A Practical Guide to Bug Resolution

Defects found during testing mean nothing if they aren't fixed. The fixing phase bridges the gap between identifying problems and delivering working software. This is where developers analyze root causes, implement solutions, and testers verify that issues are truly resolved.

Many teams underestimate this phase. They treat defect fixing as a simple back-and-forth between developers and testers. But poor fixing practices lead to missed deadlines, regression bugs, and frustrated teams. A well-structured fixing phase keeps the project moving forward without sacrificing quality.

This guide covers practical approaches to defect prioritization, efficient developer-tester collaboration, verification strategies, and the criteria for closing defects with confidence.

The fixing phase is the seventh phase in the Software Testing Life Cycle, following test execution and test reporting, and preceding test closure. The quality of defect reports from earlier phases directly impacts how quickly and accurately developers can fix issues.

Quick Answer: Defect Fixing in STLC at a Glance

Aspect	Details
What	Resolving defects identified during testing through developer fixes, tester verification, and defect closure
When	After test execution identifies defects; runs parallel to ongoing testing until release
Key Deliverables	Fixed defects, verification results, regression test results, updated defect status reports
Who	Developers fix issues; QA verifies fixes; test leads coordinate; product owners prioritize
Best For	Ensuring identified defects are resolved before release without introducing new problems

Understanding the Defect Fixing Phase

The fixing phase transforms identified problems into resolved issues. It involves more than just writing code patches. Developers must understand root causes, implement solutions that don't break other functionality, and coordinate with testers for verification.

What Happens During Defect Fixing

Root Cause Analysis: Developers investigate why defects occurred, not just what the symptoms are. A button that doesn't respond might have issues in the click handler, the event binding, network connectivity, or server-side processing. Finding the actual cause prevents partial fixes.

Code Changes: Developers modify source code, configuration, or data to address the root cause. Changes should be minimal and targeted - broad refactoring during defect fixing introduces risk.

Unit Testing: Developers verify their fixes work in isolation before passing to QA. This catches obvious problems early and reduces the back-and-forth cycle.

Build and Deploy: Fixed code gets compiled, packaged, and deployed to test environments where testers can verify the resolution.

Verification: Testers confirm that the defect no longer reproduces and that the fix works as expected across relevant scenarios.

Regression Check: Teams verify that fixes haven't broken existing functionality.

Position in STLC

The fixing phase receives inputs from test execution and test reporting:

• Defect Reports: Detailed descriptions of issues found during testing
• Reproduction Steps: Exact steps to recreate the defect
• Environment Details: Configuration where the defect occurs
• Priority Assessment: Severity and urgency ratings

The fixing phase produces outputs for test closure:

• Fixed Defects: Resolved issues verified by testing
• Deferred Defects: Issues intentionally postponed to future releases
• Resolution Documentation: Details of what was changed and why

The Defect Fixing Process

Effective defect fixing follows a structured workflow that keeps issues moving toward resolution.

Step 1: Review and Assign Defects

New defects need evaluation before developer assignment:

Validate the Defect: Confirm it's a genuine software problem, not a test case error, environment issue, or expected behavior.

Check for Duplicates: Search existing defects to avoid assigning duplicate issues to different developers.

Assess Completeness: Ensure the defect report has sufficient information for the developer to understand and reproduce the issue.

Assign to Developer: Route the defect to the appropriate developer based on component ownership, expertise, or availability.

Step 2: Analyze Root Cause

Developers investigate defects to understand underlying causes:

Reproduce the Issue: Follow the reported steps to observe the defect firsthand. This confirms the issue and provides context for investigation.

Debug and Trace: Use debugging tools, log analysis, and code inspection to trace the execution path and identify where behavior diverges from expectations.

Identify Root Cause: Distinguish between the symptom (what the user sees) and the cause (why it happens). A form validation error might stem from incorrect regex, missing null checks, encoding issues, or server-side logic problems.

Document Findings: Record what caused the defect for future reference and knowledge sharing.

Step 3: Implement the Fix

With root cause understood, developers create solutions:

Plan the Change: Determine the minimal code modification that addresses the root cause without introducing side effects.

Write the Fix: Implement the code change, following team coding standards and practices.

Add Unit Tests: Create or update unit tests to cover the defect scenario, preventing future regression.

Self-Review: Review your own changes before submitting. Check for typos, edge cases, and potential side effects.

Code Review: Submit changes for peer review. Fresh eyes catch issues the original developer might miss.

Step 4: Deploy and Verify

Fixed code needs deployment to test environments:

Build the Application: Compile the fix into a testable build.

Deploy to Test Environment: Move the build to the environment where testers can verify it.

Notify Testers: Alert the tester who reported the defect (or the verification assignee) that a fix is ready for testing.

Retest the Defect: Testers execute the original reproduction steps to confirm the issue no longer occurs.

Test Related Scenarios: Verify the fix works across browsers, devices, or data variations relevant to the defect.

Step 5: Close or Reopen

Based on verification results:

Close the Defect: If the fix works and regression checks pass, mark the defect as verified and closed.

Reopen the Defect: If the issue still reproduces or the fix introduced new problems, reopen with updated information about what was observed.

Defect Prioritization and Triage

Not all defects are equal. Prioritization ensures teams fix the most important issues first.

Severity vs. Priority

Severity measures impact on the system:

Severity	Description	Example
Critical	System crash, data corruption, security breach	Application crashes on login
High	Major feature broken, no workaround	Cannot complete checkout process
Medium	Feature partially works, workaround exists	Search filters don't work, but search still returns results
Low	Minor issue, cosmetic problem	Alignment slightly off on one screen

Priority indicates fixing urgency:

Priority	Description	Action
P1 - Critical	Blocks release or production	Fix immediately, all hands on deck
P2 - High	Must fix before release	Schedule for current sprint
P3 - Medium	Should fix, but can defer if needed	Fix if time allows
P4 - Low	Nice to have	Backlog for future release

Severity and priority don't always match. A typo in the CEO's name on the About page is low severity (cosmetic) but might be P1 priority (brand reputation). A crash in an obscure admin feature is high severity but might be P3 priority (rarely used).

Triage Process

Regular triage meetings keep defect management efficient:

Daily Triage (During Active Testing):

• Review all new defects from the past 24 hours
• Validate severity and priority assignments
• Assign defects to developers
• Identify blockers needing immediate attention

Weekly Triage (Maintenance Mode):

• Review defect backlog
• Adjust priorities based on release schedule
• Decide on deferrals
• Track resolution velocity

Triage Participants:

• Test Lead: Explains defects, answers technical questions
• Development Lead: Assigns developers, estimates effort
• Product Owner: Confirms priority from business perspective
• Scrum Master/PM: Tracks capacity, resolves conflicts

Making Deferral Decisions

Some defects won't be fixed this release. Deferral decisions should be explicit:

Valid Reasons to Defer:

• Low severity/priority relative to release timeline
• Fix requires significant architectural changes
• Workaround exists and impact is minimal
• Issue affects a feature being redesigned

Document Deferrals: Record why each defect was deferred, who approved it, and the target release for fixing. Don't let deferrals disappear into a black hole.

Communicate Deferrals: Inform stakeholders about known issues shipping with the release and their workarounds.

Developer-Tester Collaboration

Fixing defects efficiently requires smooth collaboration between developers and testers.

Writing Defect Reports That Developers Can Use

Good defect reports accelerate fixing. Poor reports create friction.

Essential Elements:

Element	Why It Matters
Clear Title	Developers scan titles to understand scope quickly
Reproduction Steps	Exact steps eliminate guesswork
Expected vs. Actual	Shows exactly what's wrong
Environment Details	Configuration affects behavior
Evidence	Screenshots and logs speed diagnosis

Good Report Example:

Title: Order total displays $0.00 when applying 100% discount coupon

Steps: 1. Add any item to cart. 2. Enter coupon code "FREESHIP100". 3. Click Apply.

Expected: Order total shows $0.00, items remain in cart

Actual: Order total shows $0.00, but cart shows "No items" message

Environment: Chrome 120, Production build 2.4.1

Bad Report Example:

Title: Cart bug

Steps: Use coupon

Expected: Should work

Actual: Doesn't work

Communication During Fixing

Stay connected throughout the fixing process:

Clarification Questions: Developers should ask questions early rather than guess. Testers should respond promptly.

Fix Progress Updates: Developers should update defect status as they work (In Progress, Under Review, Ready for Test).

Verification Feedback: Testers should provide quick feedback after verification, not let defects sit in Ready for Test status.

Reopen Discussions: When testers reopen defects, include specifics about what's still broken. "Still doesn't work" isn't helpful.

Handling Disagreements

Sometimes developers and testers disagree about defects:

"Not a Bug" Disputes: Developer believes behavior is correct. Resolution: Review requirements together. If requirements are ambiguous, involve the product owner.

"Cannot Reproduce" Issues: Developer can't recreate the defect. Resolution: Get on a call and have the tester demonstrate. Check environment differences.

Priority Disagreements: Developer thinks defect isn't urgent. Resolution: Escalate to triage. Let stakeholders decide based on business impact.

Keep disagreements professional. Both developers and testers want quality software - they just have different perspectives.

Verification and Retesting

Verification confirms that fixes actually work. Rushing verification undermines the entire fixing effort.

Retesting the Fixed Defect

When a fix is ready for verification:

1. Verify Environment: Confirm you're testing the correct build with the fix included. Check version numbers or build timestamps.

2. Reproduce Original Steps: Execute the exact reproduction steps from the defect report. Don't vary the steps initially.

3. Confirm Resolution: Verify the defect no longer occurs. The actual result should now match the expected result.

4. Test Variations: Try related scenarios that might exercise the same code path. Different data values, different user roles, different browsers.

5. Document Results: Record what you tested and what you observed. Update defect status based on results.

When to Reopen Defects

Reopen a defect if:

• The original issue still reproduces
• The fix works partially but not completely
• The fix introduced new related problems
• The fix works in one environment but not another

When reopening, provide new information:

• Confirm you're testing the correct build
• Describe exactly what you observed
• Note any differences from the original behavior
• Include fresh screenshots or logs

Verification vs. New Defects

Distinguish between fix failures and new issues:

Fix Failure: The original defect still exists or the specific fix doesn't work. Reopen the existing defect.

Related New Issue: The fix works, but revealed a different problem. Create a new defect and link it to the original.

Unrelated New Issue: Something else broke that wasn't related to this fix. Create a new defect without linking (unless evidence suggests connection).

Regression Testing After Fixes

Every fix carries regression risk. Code changes might break functionality that was working before.

Why Regression Testing Matters

Fixes modify code. Modified code can:

• Break features that depend on the changed code
• Alter shared functions used by other features
• Change database schemas or data formats
• Affect integration points with other systems

Regression testing catches these problems before they reach production.

Regression Testing Approaches

Focused Regression: Test areas directly related to the fix. If you fixed checkout logic, regression test payment processing, order confirmation, and inventory updates.

Full Regression: Run the complete regression suite. Appropriate for major fixes or late in the release cycle.

Risk-Based Regression: Prioritize regression tests based on:

• Components modified by the fix
• Integration points affected
• Features with historical instability
• High-business-impact functionality

Automated Regression: Run automated test suites after each fix. Automation provides fast, consistent regression coverage.

Handling Regression Failures

When regression tests fail after a fix:

1. Confirm It's a Regression: Verify the test passed before the fix. Check if the test is flaky or the test environment changed.

2. Assess Impact: Determine severity. Did the fix break critical functionality or minor edge cases?

3. Decide on Action:

• Revert the fix and try again
• Fix the regression bug
• Accept the regression (rare, requires stakeholder approval)

4. Log New Defect: Create a defect for the regression, linked to the original fix.

Entry and Exit Criteria

Entry and exit criteria establish quality gates for the fixing phase.

Entry Criteria

Before fixing begins:

• Test execution has produced defects requiring fixes
• Defect reports are logged with sufficient detail
• Developers are available and assigned to defects
• Test environment is available for verification
• Defect tracking system is configured and accessible
• Triage process is established

Exit Criteria

Before moving to test closure:

• All critical-priority defects are fixed and verified
• All high-priority defects are fixed, verified, or explicitly deferred with stakeholder approval
• Medium and low priority defects are fixed, deferred, or accepted as known issues
• Regression testing completed with acceptable results
• Defect status reports are current and accurate
• No defects remain in "Ready for Test" status
• Deferral decisions are documented and communicated

When Criteria Aren't Met

If exit criteria can't be achieved:

Document Gaps: Record which criteria aren't met and why.

Assess Risk: Evaluate the risk of proceeding with unresolved defects.

Get Approval: Obtain stakeholder sign-off on proceeding despite unmet criteria.

Communicate Known Issues: Ensure release notes include any unresolved defects.

Common Challenges and Solutions

Real-world fixing phases encounter predictable obstacles.

Challenge: Defects Can't Be Reproduced

Developers can't recreate the issue testers reported.

Solutions:

• Have tester demonstrate the defect live
• Compare test and development environments
• Check if the defect is intermittent or timing-dependent
• Review logs from when the defect occurred
• Use screen recordings to capture reproduction

Challenge: Fixes Keep Breaking Other Things

Every fix introduces new regressions.

Solutions:

• Improve unit test coverage before fixing
• Require code review for all fixes
• Increase regression test coverage in problem areas
• Consider if the code needs refactoring, not patching
• Implement integration tests around fragile components

Challenge: Defect Backlog Grows Faster Than Fixes

More defects are found than fixed.

Solutions:

• Prioritize ruthlessly - focus on critical and high
• Add development resources if available
• Defer low-priority defects explicitly
• Reduce scope if timeline is fixed
• Address root causes of defect density

Challenge: Verification Takes Too Long

Defects sit in "Ready for Test" queue indefinitely.

Solutions:

• Assign dedicated verification time daily
• Notify testers immediately when fixes are ready
• Reduce test environment setup time
• Parallelize verification across team members
• Automate verification where possible

Challenge: Scope Creep in Fixes

Developers expand fixes beyond the defect scope, adding features or refactoring code.

Solutions:

• Keep fixes minimal and targeted
• Require separate tickets for enhancements
• Review fix scope during code review
• Distinguish between fixes and improvements in tracking

Best Practices for Effective Defect Fixing

These practices consistently improve fixing phase effectiveness.

Fix Root Causes, Not Symptoms

A quick patch might make the defect pass testing, but the underlying problem remains. Invest time to understand why defects occur.

Example: A null pointer exception might be "fixed" with a null check, but the root cause might be a race condition in data loading. The null check hides the symptom while the race condition causes other problems.

Keep Fixes Small and Focused

Large code changes are:

• Harder to review
• More likely to introduce regressions
• More difficult to roll back
• Slower to verify

Fix exactly what's broken. Save refactoring and improvements for separate work items.

Test Your Own Fixes

Developers should verify fixes work before passing to QA:

• Run the reproduction steps yourself
• Execute relevant unit tests
• Check for obvious side effects
• Confirm the build succeeds

This catches basic problems early and shows respect for testers' time.

Communicate Fix Readiness Clearly

Ambiguous fix status creates confusion:

• "In Progress" means actively working on it
• "In Review" means code review pending
• "Ready for Test" means deployed and verifiable
• Don't mark "Ready for Test" until it's actually deployed

Track Everything

Document what was changed and why:

• Link code commits to defects
• Record root cause analysis findings
• Note any unusual decisions or workarounds
• Update defect comments with progress

This documentation helps future debugging and knowledge transfer.

Metrics for Tracking Fixing Progress

Metrics provide visibility into fixing phase health.

Key Metrics

Metric	Calculation	Purpose
Fix Rate	Defects fixed / Total open defects	Measures resolution velocity
Verification Rate	Defects verified / Defects ready for test	Shows verification throughput
Reopen Rate	Defects reopened / Defects verified	Indicates fix quality
Defect Age	Days from open to close	Tracks resolution time
Fix Turnaround	Days from assigned to ready for test	Measures developer response
Backlog Trend	Open defects over time	Shows if backlog is growing or shrinking

Using Metrics Effectively

Trending Matters More Than Snapshots: A single day's metrics can mislead. Track trends over time to see if things are improving or degrading.

Don't Optimize for Metrics: If teams are evaluated on defect closure counts, they might close defects without proper verification or mark issues as "by design" inappropriately.

Investigate Anomalies: Unusually high reopen rates, growing backlogs, or long defect ages signal problems worth investigating.

Share Metrics Transparently: Display metrics on team dashboards so everyone sees the current state and progress.

Conclusion

The defect fixing phase transforms test findings into software improvements. Success requires more than good developers and thorough testers - it requires structured processes, clear communication, and disciplined verification.

Remember these principles:

Prioritize Ruthlessly: Not all defects need immediate fixing. Use severity and priority to focus effort where it matters most.

Collaborate Actively: Developers and testers work toward the same goal. Direct communication and mutual respect accelerate fixing.

Verify Thoroughly: A fix isn't complete until it's verified. Rushed verification leads to reopened defects and wasted cycles.

Manage Regression Risk: Every fix can break something else. Appropriate regression testing protects existing functionality.

Track Progress Transparently: Metrics and status reports keep stakeholders informed and help teams identify problems early.

The fixing phase often determines whether projects meet their release dates. Teams that handle defect fixing efficiently deliver on time without sacrificing quality. Teams that struggle with fixing face crunch periods, escaped defects, and frustrated stakeholders.

Build on the defect reports from test execution and test reporting, execute a disciplined fixing process, and set up your team for smooth test closure.

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