Test Levels Framework

Comprehensive guide for determining appropriate test levels (unit, integration, E2E) for different scenarios.

Test Level Decision Matrix

Unit Tests

When to use:

• Testing pure functions and business logic
• Algorithm correctness
• Input validation and data transformation
• Error handling in isolated components
• Complex calculations or state machines

Characteristics:

• Fast execution (immediate feedback)
• No external dependencies (DB, API, file system)
• Highly maintainable and stable
• Easy to debug failures

Example scenarios:

unit_test:
  component: 'PriceCalculator'
  scenario: 'Calculate discount with multiple rules'
  justification: 'Complex business logic with multiple branches'
  mock_requirements: 'None - pure function'

Integration Tests

When to use:

• Component interaction verification
• Database operations and transactions
• API endpoint contracts
• Service-to-service communication
• Middleware and interceptor behavior

Characteristics:

• Moderate execution time
• Tests component boundaries
• May use test databases or containers
• Validates system integration points

Example scenarios:

integration_test:
  components: ['UserService', 'AuthRepository']
  scenario: 'Create user with role assignment'
  justification: 'Critical data flow between service and persistence'
  test_environment: 'In-memory database'

End-to-End Tests

When to use:

• Critical user journeys
• Cross-system workflows
• Visual regression testing
• Compliance and regulatory requirements
• Final validation before release

Characteristics:

• Slower execution
• Tests complete workflows
• Requires full environment setup
• Most realistic but most brittle

Example scenarios:

e2e_test:
  journey: 'Complete checkout process'
  scenario: 'User purchases with saved payment method'
  justification: 'Revenue-critical path requiring full validation'
  environment: 'Staging with test payment gateway'

Test Level Selection Rules

Favor Unit Tests When:

• Logic can be isolated
• No side effects involved
• Fast feedback needed
• High cyclomatic complexity

Favor Integration Tests When:

• Testing persistence layer
• Validating service contracts
• Testing middleware/interceptors
• Component boundaries critical

Favor E2E Tests When:

• User-facing critical paths
• Multi-system interactions
• Regulatory compliance scenarios
• Visual regression important

Anti-patterns to Avoid

• E2E testing for business logic validation
• Unit testing framework behavior
• Integration testing third-party libraries
• Duplicate coverage across levels

Duplicate Coverage Guard

Before adding any test, check:

1. Is this already tested at a lower level?
2. Can a unit test cover this instead of integration?
3. Can an integration test cover this instead of E2E?

Coverage overlap is only acceptable when:

• Testing different aspects (unit: logic, integration: interaction, e2e: user experience)
• Critical paths requiring defense in depth
• Regression prevention for previously broken functionality

Test Naming Conventions

• Unit: test_{component}_{scenario}
• Integration: test_{flow}_{interaction}
• E2E: test_{journey}_{outcome}

Test ID Format

{EPIC}.{STORY}-{LEVEL}-{SEQ}

Examples:

• 1.3-UNIT-001
• 1.3-INT-002
• 1.3-E2E-001