regression-testing

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 |

---

```typescript

// Analyze changed files and select impacted tests

function selectTests(changedFiles: string[]): string[] {

const testsToRun = new Set();

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

```

---

```

/\

/ \ 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)

```

---

```yaml

# .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

```

---

```javascript

// 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

```

---

```typescript

// 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");

```

---

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

```typescript

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'

});

```

---

• [risk-based-testing](../risk-based-testing/) - Risk-based prioritization
• [test-automation-strategy](../test-automation-strategy/) - Automation pyramid
• [continuous-testing-shift-left](../continuous-testing-shift-left/) - CI/CD integration

---

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.