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pantheon-ai/test-driven-development

Master Test-Driven Development with deterministic red-green-refactor workflows, test-first feature delivery, bug reproduction through failing tests, behavior-focused assertions, and refactoring safety; use when implementing new functions, changing APIs, fixing regressions, or restructuring code under test.

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strat-test-pyramid.mdreferences/

title:
Follow the Test Pyramid
impact:
LOW
impactDescription:
reduces test infrastructure cost by 10-100×
tags:
strat, pyramid, distribution, balance

Follow the Test Pyramid

Distribute tests according to the pyramid: many unit tests at the base, fewer integration tests in the middle, and minimal E2E tests at the top.

Incorrect (inverted pyramid):

┌─────────────────────────────┐
           │      E2E Tests (500)        │  ← Slow, expensive, flaky
           ├─────────────────────────────┤
           │   Integration Tests (100)   │
           ├─────────────────────────────┤
           │    Unit Tests (50)          │  ← Fast, cheap, stable
           └─────────────────────────────┘

Test run time: 45 minutes
Maintenance cost: HIGH
Flakiness: FREQUENT
Infrastructure cost: $10,000/month

Correct (proper pyramid):

┌───────────┐
                    │ E2E (20)  │  ← Critical user journeys only
                ┌───┴───────────┴───┐
                │ Integration (100)  │  ← Component boundaries
            ┌───┴───────────────────┴───┐
            │     Unit Tests (500)       │  ← Business logic
            └───────────────────────────┘

Test run time: 5 minutes
Maintenance cost: LOW
Flakiness: RARE
Infrastructure cost: $100/month

Distribution guidelines:

LayerCountScopeSpeed
Unit70-80%Single function/class<100ms
Integration15-25%Multiple components<5s
E2E5-10%Full user journey<30s

What to test at each level:

  • Unit: Business logic, calculations, transformations
  • Integration: API contracts, database queries, service interactions
  • E2E: Critical user paths, smoke tests, happy paths

Reference: The Practical Test Pyramid - Martin Fowler

Install with Tessl CLI

npx tessl i pantheon-ai/test-driven-development

references

assert-custom-matchers.md

assert-error-messages.md

assert-no-assertions-antipattern.md

assert-snapshot-testing.md

assert-specific-assertions.md

cycle-maintain-test-list.md

cycle-minimal-code-to-pass.md

cycle-refactor-after-green.md

cycle-small-increments.md

cycle-verify-test-fails-first.md

cycle-write-test-first.md

data-avoid-mystery-guests.md

data-builder-pattern.md

data-minimal-setup.md

data-unique-identifiers.md

data-use-factories.md

design-aaa-pattern.md

design-avoid-logic-in-tests.md

design-descriptive-test-names.md

design-one-assertion-per-test.md

design-test-behavior-not-implementation.md

design-test-edge-cases.md

isolate-deterministic-tests.md

isolate-mock-external-dependencies.md

isolate-no-shared-state.md

isolate-prefer-stubs-over-mocks.md

isolate-use-dependency-injection.md

org-file-structure.md

org-group-by-behavior.md

org-parameterized-tests.md

org-setup-teardown.md

org-test-utilities.md

perf-avoid-network-calls.md

perf-avoid-sleep.md

perf-fast-unit-tests.md

perf-fix-flaky-tests.md

perf-parallelize-tests.md

strat-coverage-targets.md

strat-e2e-critical-paths.md

strat-integration-boundaries.md

strat-mutation-testing.md

strat-test-pyramid.md

SKILL.md

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