Test Strategy: ROI-Based Selection

Core Principle: Maximum Coverage, Minimum Tests

Philosophy: 10 reliable tests > 100 unmaintained tests

Quality over quantity - focus resources on high-value tests that provide maximum coverage with minimum maintenance burden.

ROI Calculation Framework

ROI Formula

ROI Score = (Business Value × User Frequency + Legal Requirement × 10 + Defect Detection)
            / (Creation Cost + Execution Cost + Maintenance Cost)

Value Components

Business Value (0-10 scale):

• 10: Revenue-critical (payment processing, checkout)
• 8-9: Core business features (user registration, data persistence)
• 5-7: Important secondary features (search, filtering)
• 2-4: Nice-to-have features (UI enhancements)
• 0-1: Cosmetic features

User Frequency (0-10 scale):

• 10: Every user, every session (authentication)
• 8-9: >80% of users regularly
• 5-7: 50-80% of users occasionally
• 2-4: <50% of users rarely
• 0-1: Edge case users only

Legal Requirement (boolean → 0 or 1):

• 1: Legally mandated (GDPR compliance, data protection)
• 0: Not legally required

Defect Detection (0-10 scale):

• 10: High likelihood of catching critical bugs
• 5-7: Moderate likelihood of catching bugs
• 0-4: Low likelihood (simple logic, well-tested patterns)

Cost Components

Test Level Cost Table:

Test Level	Creation Cost	Execution Cost	Maintenance Cost	Total Cost
Unit	1	1	1	3
Integration	3	5	3	11
E2E	10	20	8	38

Cost Rationale:

• Unit Tests: Fast to write, fast to run, rarely break from refactoring
• Integration Tests: Moderate setup, slower execution, moderate maintenance
• E2E Tests: Complex setup, very slow execution, high brittleness (12x more expensive than unit tests)

ROI Calculation Examples

Example 1: Payment Processing Integration Test

Business Value: 10 (revenue-critical)
User Frequency: 9 (90% of users)
Legal Requirement: 0
Defect Detection: 8 (high complexity)

ROI = (10 × 9 + 0 + 8) / 11 = 98 / 11 = 8.9
Decision: HIGH ROI → Generate this test

Example 2: UI Theme Toggle E2E Test

Business Value: 2 (cosmetic feature)
User Frequency: 5 (50% of users)
Legal Requirement: 0
Defect Detection: 3 (simple logic)

ROI = (2 × 5 + 0 + 3) / 38 = 13 / 38 = 0.34
Decision: LOW ROI → Skip this E2E test (consider unit test instead)

Example 3: GDPR Data Deletion E2E Test

Business Value: 8 (critical compliance)
User Frequency: 1 (rare user action)
Legal Requirement: 1 (legally mandated)
Defect Detection: 9 (high consequences if broken)

ROI = (8 × 1 + 1 × 10 + 9) / 38 = 27 / 38 = 0.71
Decision: MEDIUM ROI → Generate (legal requirement justifies cost)

Critical User Journey Definition

Tests with HIGH priority regardless of strict ROI calculation:

Mandatory Coverage Areas

1. Revenue-Impacting Flows

   • Payment processing end-to-end
   • Checkout and order completion
   • Subscription management
   • Purchase confirmation and receipts

2. Legally Required Flows

   • GDPR data deletion/export
   • User consent management
   • Data protection compliance
   • Regulatory audit trails

3. High-Frequency Core Functionality

   • User authentication/authorization (>80% of users)
   • Core CRUD operations for primary entities
   • Critical business workflows
   • Data integrity for primary data models

Budget Exception: Critical User Journeys may exceed standard budget limits with explicit justification.

Test Selection Guidelines

Selection Thresholds

Integration Tests:

• ROI > 3.0: Strong candidate
• ROI 1.5-3.0: Consider based on available budget
• ROI < 1.5: Skip or convert to unit test

E2E Tests:

• ROI > 2.0: Strong candidate
• ROI 1.0-2.0: Consider if Critical User Journey
• ROI < 1.0: Skip (too expensive relative to value)

Push-Down Analysis

Before generating higher-level test, ask:

1. Can this be unit-tested?

   • YES → Generate unit test instead
   • NO → Continue to integration test consideration

2. Already covered by integration test?

   • YES → Don't create E2E version
   • NO → Consider E2E test if ROI justifies

Example:

• "Tax calculation accuracy" → Unit test (pure logic)
• "Tax applied to order total" → Integration test (multiple components)
• "User sees correct tax in checkout flow" → E2E test only if Critical User Journey

Deduplication Strategy

Before generating any test:

1. Search existing test suite for similar coverage
2. Check for overlapping scenarios at different test levels
3. Identify redundant verifications already covered elsewhere

Decision Matrix:

Existing coverage found?
  → Full coverage: Skip new test
  → Partial coverage: Extend existing test
  → No coverage: Generate new test

Application in Test Generation

Phase 1: Candidate Enumeration

• List all possible test scenarios
• Assign ROI metadata to each candidate

Phase 2: ROI-Based Selection

1. Calculate ROI for each candidate
2. Apply deduplication checks
3. Apply push-down analysis
4. Sort by ROI (descending)

Phase 3: Budget Enforcement

• Select top N tests within budget limits
• Document budget usage
• Report selection rationale

See: .agents/tasks/acceptance-test-generation.md for detailed implementation process

Continuous Improvement

Metrics to Track

1. Selection Rate: Tests generated / Total candidates

   • Target: 25-35% (indicates effective filtering)

2. Average ROI: Average ROI of generated tests

   • Target: >3.0 for integration, >1.5 for E2E

3. Budget Utilization: Actual tests / Budget limit

   • Target: 80-100% (full utilization of valuable test slots)

4. Defect Detection Rate: Bugs caught / Total tests

   • Track over time to validate ROI predictions

Calibration

Periodically review:

• Are high-ROI tests actually catching bugs?
• Are cost estimates accurate?
• Do business value ratings align with stakeholder priorities?

Adjust formula weights based on empirical data

Anti-Patterns to Avoid

❌ Gaming the System:

• Inflating business value scores to justify favorite tests
• Ignoring ROI when it contradicts intuition
• Cherry-picking ROI calculation only for preferred tests

✅ Proper Usage:

• Apply ROI calculation consistently to all candidates
• Document justification when overriding ROI decisions
• Use empirical data to calibrate scores over time

❌ Analysis Paralysis:

• Spending excessive time on precise ROI calculations
• Debating single-point differences in scores
• Treating ROI as exact science rather than decision aid

✅ Practical Application:

• Use ROI for relative prioritization, not absolute precision
• Focus on order-of-magnitude differences (8.9 vs 0.34)
• Make quick decisions for obvious high/low ROI cases