ref-testing-pyramid

name	ref-testing-pyramid
description	Test pyramid strategy, coverage targets, test patterns, and quality metrics reference. Agent-extending skill that amplifies expert-testing and manager-tdd expertise with production-grade testing patterns. NOT for: production code implementation, architecture design, DevOps, security audits.
user-invocable	false
metadata	{"version":"1.0.0","category":"domain","status":"active","updated":"2026-03-30","tags":"testing, pyramid, coverage, tdd, patterns, reference","agent":"expert-testing"}
progressive_disclosure	{"enabled":true,"level1_tokens":100,"level2_tokens":3000}
triggers	{"keywords":["test","coverage","tdd","unit test","integration","e2e"],"agents":["expert-testing","manager-tdd"],"phases":["run"]}

Testing Pyramid Reference

Target Agents

• expert-testing - Primary: applies patterns during test creation and coverage analysis
• manager-tdd - Secondary: applies during RED-GREEN-REFACTOR cycles

Test Pyramid Ratios

       /  E2E  \        10% — Critical user journeys only
      /----------\
     / Integration \    20% — API endpoints, DB queries, service boundaries
    /----------------\
   /    Unit Tests    \  70% — Functions, hooks, utilities, pure logic
  /--------------------\

Level	Speed	Reliability	Maintenance	Coverage Target
Unit	Fast (<100ms)	High	Low	70% of tests
Integration	Medium (1-5s)	Medium	Medium	20% of tests
E2E	Slow (10-60s)	Lower	High	10% of tests

Coverage Targets by Context

Context	Target	Rationale
Critical business logic	95%+	Revenue/security impact
API endpoints	90%+	Contract compliance
Utility functions	85%+	Reuse reliability
UI components	80%+	Rendering correctness
Configuration/glue code	60%+	Low complexity
Generated code	0%	Don't test generated code

Test Pattern: AAA (Arrange-Act-Assert)

// Arrange: Set up test data and preconditions
input := CreateTestUser("[e-mail]")

// Act: Execute the function under test
result, err := service.CreateUser(ctx, input)

// Assert: Verify the outcome
assert.NoError(t, err)
assert.Equal(t, "[e-mail]", result.Email)

Unit Test Patterns

Pattern	When	Example
Table-Driven	Multiple input/output combinations	Go: tests := []struct{...}
Mock/Stub	External dependencies (DB, API)	Interface injection, mock frameworks
Snapshot	Complex output comparison	Jest snapshots, golden files
Property-Based	Mathematical properties	quickcheck, hypothesis
Boundary Value	Edge cases	0, -1, MAX_INT, empty string, nil

Integration Test Patterns

Pattern	When	Example
Testcontainers	Real DB needed	Docker-based PostgreSQL for tests
HTTP Test Server	API endpoint testing	httptest.NewServer (Go), supertest (Node)
In-Memory DB	Fast DB tests	SQLite for development
Fixture Loading	Consistent test data	Factory functions, seed files

What to Test vs What NOT to Test

ALWAYS Test

• Business logic and calculations
• Input validation and error handling
• Authentication and authorization flows
• Data transformations and mappings
• Edge cases and boundary conditions
• Race conditions (with -race flag in Go)

NEVER Test

• Framework internals (React rendering, Express routing)
• Third-party library behavior
• Simple getters/setters with no logic
• Private methods directly (test via public API)
• Generated code (protobuf, swagger)
• CSS styling and layout (use visual regression tools instead)

Test Quality Metrics

Metric	Target	Tool
Line Coverage	85%+	go test -cover, istanbul, coverage.py
Branch Coverage	75%+	go test -covermode=count
Mutation Score	70%+	go-mutesting, Stryker
Test Execution Time	<2 min (unit), <10 min (all)	CI timer
Flaky Test Rate	<1%	CI history analysis

Test File Conventions

Language	Test File	Location
Go	*_test.go	Same package
TypeScript	*.test.ts / *.spec.ts	__tests__/ or co-located
Python	test_*.py	tests/ directory
Java	*Test.java	src/test/ mirror
Rust	#[cfg(test)] mod tests	Same file or tests/

TDD RED-GREEN-REFACTOR Quick Reference

RED:     Write a failing test that defines expected behavior
GREEN:   Write minimal code to make the test pass
REFACTOR: Clean up while keeping tests green

Rules:

• Never write production code without a failing test
• Write the smallest test that fails
• Write the simplest code that passes
• Refactor only when all tests are green
• One assertion per test (when practical)

Common Rationalizations

Rationalization	Reality
"E2E tests cover everything, unit tests are redundant"	E2E tests are slow and flaky. Unit tests provide fast, precise feedback. The pyramid exists because each level serves a different purpose.
"Integration tests are more realistic than unit tests"	Realism comes at the cost of speed and isolation. A balanced pyramid gives both fast feedback and realistic validation.
"100% code coverage means the code is well tested"	Coverage measures execution, not correctness. A test that executes code without meaningful assertions provides zero value.
"Mocking is bad, I prefer real dependencies"	Real dependencies make tests slow and non-deterministic. Mock at boundaries, test business logic in isolation.
"This test is flaky, but it catches real bugs sometimes"	Flaky tests erode trust in the entire suite. Fix the flakiness or quarantine the test with a tracking issue.

DAMP over DRY: Test code should be descriptive and self-contained. A reader should understand the test without reading shared fixtures or helper methods.

Red Flags

• Test pyramid inverted: more E2E tests than unit tests
• Unit tests depend on external services (databases, APIs, file systems)
• Test assertions check implementation details instead of behavior
• No integration tests between unit and E2E layers
• Flaky test present without a quarantine label or tracking issue

Verification

• Test distribution follows the pyramid: unit > integration > E2E (show test counts per category)
• Unit tests run in under 30 seconds total
• Integration tests mock external dependencies at the boundary
• No flaky tests in the active suite (run 3x to verify stability)
• Test names describe behavior, not implementation (review naming convention)
• Coverage report shows meaningful assertions, not just line execution