Regression Testing

<default_to_action> When verifying changes don't break existing functionality:

• ANALYZE what changed (git diff, impact analysis)

• SELECT tests based on change + risk (not everything)

• RUN in priority order (smoke → selective → full)

• OPTIMIZE execution (parallel, sharding)

• MONITOR suite health (flakiness, execution time)

Quick Regression Strategy:

• Per-commit: Smoke + changed code tests (5-10 min)

• Nightly: Extended regression (30-60 min)

• Pre-release: Full regression (2-4 hours)

Critical Success Factors:

• Smart selection catches 90% of regressions in 10% of time

• Flaky tests waste more time than they save

• Every production bug becomes a regression test </default_to_action>

Quick Reference Card

When to Use

• After any code change

• Before release

• After dependency updates

• After environment changes

Regression Types

Type When Scope

Corrective No code change Full suite

Progressive New features Existing + new

Selective Specific changes Changed + dependent

Complete Major refactor Everything

Test Selection Strategies

Strategy How Reduction

Change-based Git diff analysis 70-90%

Risk-based Priority by impact 50-70%

Historical Frequently failing 40-60%

Time-budget Fixed time window Variable

Change-Based Test Selection

// Analyze changed files and select impacted tests function selectTests(changedFiles: string[]): string[] { const testsToRun = new Set<string>();

for (const file of changedFiles) { // Direct tests testsToRun.add(${file.replace('.ts', '.test.ts')});

// Dependent tests (via coverage mapping)
const dependentTests = testCoverage[file] || [];
dependentTests.forEach(t => testsToRun.add(t));

}

return Array.from(testsToRun); }

// Example: payment.ts changed // Runs: payment.test.ts, checkout.integration.test.ts, e2e/purchase.test.ts

Regression Suite Pyramid

     /\
    /  \  Full Regression (weekly)
   /    \  - All tests (2-4 hours)
  /------\
 /        \  Extended Regression (nightly)
/          \  - Unit + integration + critical E2E (30-60 min)

/------------
/ \ Quick Regression (per commit) /________________\ - Changed code + smoke tests (5-10 min)

CI/CD Integration

.github/workflows/regression.yml

jobs: quick-regression: runs-on: ubuntu-latest timeout-minutes: 15 steps: - name: Analyze changes id: changes uses: dorny/paths-filter@v2 with: filters: | payment: - 'src/payment/' auth: - 'src/auth/'

  - name: Run affected tests
    run: npm run test:affected

  - name: Smoke tests (always)
    run: npm run test:smoke

nightly-regression: if: github.event_name == 'schedule' timeout-minutes: 120 steps: - run: npm test -- --coverage

Optimization Techniques

// 1. Parallel execution module.exports = { maxWorkers: '50%', // Use half CPU cores testTimeout: 30000 };

// 2. Sharding across CI workers // npm test -- --shard=1/4

// 3. Incremental testing (only changed since last run) // Track last run state, skip passing unchanged tests

// 4. Fast-fail on smoke // Run critical tests first, abort if they fail

Agent-Driven Regression

// Smart test selection await Task("Regression Analysis", { pr: 1234, strategy: 'change-based-with-risk', timeBudget: '15min' }, "qe-regression-risk-analyzer");

// Returns: // { // mustRun: ['payment.test.ts', 'checkout.integration.test.ts'], // shouldRun: ['order.test.ts'], // canSkip: ['profile.test.ts', 'search.test.ts'], // estimatedTime: '12 min', // riskCoverage: 0.94 // }

// Generate regression test from production bug await Task("Bug Regression Test", { bug: { id: 'BUG-567', description: 'Checkout fails > 100 items' }, preventRecurrence: true }, "qe-test-generator");

Agent Coordination Hints

Memory Namespace

aqe/regression-testing/ ├── test-selection/* - Impact analysis results ├── suite-health/* - Flakiness, timing trends ├── coverage-maps/* - Test-to-code mapping └── bug-regressions/* - Tests from production bugs

Fleet Coordination

const regressionFleet = await FleetManager.coordinate({ strategy: 'comprehensive-regression', agents: [ 'qe-regression-risk-analyzer', // Analyze changes, select tests 'qe-test-executor', // Execute selected tests 'qe-coverage-analyzer', // Analyze coverage gaps 'qe-quality-gate' // Go/no-go decision ], topology: 'sequential' });

Related Skills

• risk-based-testing - Risk-based prioritization

• test-automation-strategy - Automation pyramid

• continuous-testing-shift-left - CI/CD integration

Remember

Regression testing is insurance against change. Every code change is a risk. Smart regression testing mitigates that risk by testing what matters based on what changed.

Good regression testing is strategic, not exhaustive. You cannot test everything, every time. Select based on changes, risk, and time budget.

With Agents: qe-regression-risk-analyzer provides intelligent test selection achieving 90% defect detection in 10% of execution time. Agents generate regression tests from production bugs automatically.