Integration and E2E Testing Principles

Test Type Definition and Limits

Test Type	Purpose	Scope	Limit per Feature	Implementation Timing
Integration	Verify component interactions	Partial system integration	MAX 3	Created alongside implementation
E2E	Verify critical user journeys	Full system	MAX 1-2	Executed in final phase only

Behavior-First Principle

Include (High ROI)

•Business logic correctness (calculations, state transitions, data transformations)
•Data integrity and persistence behavior
•User-visible functionality completeness
•Error handling behavior (what user sees/experiences)

Exclude (Low ROI in CI/CD)

•External service real connections → Use contract/interface verification
•Performance metrics → Non-deterministic, defer to load testing
•Implementation details → Focus on observable behavior
•UI layout specifics → Focus on information availability

Principle: Test = User-observable behavior verifiable in isolated CI environment

ROI Calculation

code

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

Cost Table

Test Type	Create	Execute	Maintain	Total
Unit	1	1	1	3
Integration	3	5	3	11
E2E	10	20	8	38

Test Skeleton Specification

Required Comment Patterns

Each test MUST include the following annotations:

code

// AC: [Original acceptance criteria text]
// Behavior: [Trigger] → [Process] → [Observable Result]
// @category: core-functionality | integration | edge-case | e2e
// @dependency: none | [component names] | full-system
// @complexity: low | medium | high
// ROI: [score]

Verification Items (Optional)

When verification points need explicit enumeration:

code

// Verification items:
// - [Item 1]
// - [Item 2]

EARS Format Mapping

EARS Keyword	Test Type	Generation Approach
When	Event-driven	Trigger event → verify outcome
While	State condition	Setup state → verify behavior
If-then	Branch coverage	Both condition paths verified
(none)	Basic functionality	Direct invocation → verify result

Test File Naming Convention

•Integration tests: *.int.test.* or *.integration.test.*
•E2E tests: *.e2e.test.*

The test runner or framework in the project determines the appropriate file extension.

Review Criteria

Skeleton and Implementation Consistency

Check	Failure Condition
Behavior Verification	No assertion for "observable result" in skeleton
Verification Item Coverage	Listed items not all covered by assertions
Mock Boundary	Internal components mocked in integration test

Implementation Quality

Check	Failure Condition
AAA Structure	Arrange/Act/Assert separation unclear
Independence	State sharing between tests, order dependency
Reproducibility	Date/random dependency, varying results
Readability	Test name doesn't match verification content

Quality Standards

Required

•Each test verifies one behavior
•Clear AAA (Arrange-Act-Assert) structure
•No test interdependencies
•Deterministic execution

Prohibited

•Testing implementation details
•Multiple behaviors per test
•Shared mutable state
•Time-dependent assertions without mocking

Property-Based Testing

Property-based testing generates random inputs to verify invariants that should hold for ALL possible values, not just specific test cases.

When to Apply

Scenario	Property Example
Sorting algorithms	`sort(arr).length === arr.length` AND each element <= next
Serialization	`decode(encode(value)) === value` for any valid value
Data transformations	`transform(transform_inverse(x)) === x`
Validation functions	Valid inputs always pass, structurally invalid inputs always fail
Mathematical operations	Commutativity, associativity, distributivity
Collection operations	Map preserves length, filter reduces or preserves length

Property Test Structure (Language-Agnostic)

code

PROPERTY: "Description of the invariant"
FOR ALL: generator description (e.g., "arbitrary arrays of integers, length 0-1000")
ASSERT: invariant expression
SHRINK: how to minimize failing cases

Example:
  PROPERTY: "Sorting preserves all elements"
  FOR ALL: arrays of comparable elements
  ASSERT:
    - sorted.length === original.length
    - every element in original exists in sorted
    - sorted[i] <= sorted[i+1] for all valid i
  SHRINK: reduce array size until minimal failing case found

ROI Assessment for Property Tests

Factor	Score Guidance
Input space size	Large (>100 meaningful variations) → High ROI
Bug severity if invariant broken	Data corruption / security → High ROI
Implementation complexity	Simple property → High ROI
Existing coverage	No edge case coverage → High ROI

Minimum ROI threshold: Only create property tests when at least 2 factors score High.

Integration with Test Budget

Property tests count toward the integration test budget. Each property test replaces approximately 5-10 specific input unit tests, making them highly budget-efficient for the right scenarios.