# TDD Foundation — Design Spec

> **Note (2026-05-05, post-Plan-8):** File-path references in this spec describe the **pre-Plan-8 layout**. Plan 8 (Lazar pattern conformance) introduced `entities/models/`, `entities/errors/<domain>.ts`, the `.mock.ts` suffix, dropped `payload-` prefixes, and made use cases / controllers factory functions. The TDD principles, gap catalogue, and `core-testing` package design remain valid; only the example paths and snippets shifted. See `docs/superpowers/refactor-logs/2026-05-05-lazar-pattern-conformance.md` and ADR-012 for the mapping.

**Date:** 2026-05-05
**Status:** Approved
**Author:** Claude Opus 4.7 (1M context)
**Reviewer:** Danijel
**Supersedes:** none — extends `2026-04-21-vertical-monorepo-refactor-design.md` §13B

---

## 1. Goal

Make full TDD the path of least resistance in this monorepo so that agentic workers (and humans) cannot produce production code without first writing a failing test. Close the ten gaps catalogued in §3.

The success criterion is operational, not aspirational: a fresh subagent given any plan task in this template should hit a failing test before they touch production code, and a human reviewer should be able to read a single guide (`docs/guides/tdd-workflow.md`) and the per-feature `AGENTS.md` to understand why each test exists.

## 2. Non-goals

- Mutation testing (deferred — Tier 3)
- Visual regression beyond Storybook smoke (deferred — Tier 3)
- Property-based testing (deferred)
- Replacing existing passing tests (we extend the test suite, we do not rewrite working tests for stylistic reasons)
- Docker-in-CI for full Payload integration tests (mock at `payload` module boundary instead — much faster, and the contract suite catches drift)

## 3. The ten gaps

| # | Gap | Closed by |
|---|-----|-----------|
| 1 | Zero tests in `core-ui`, `core-api`, `core-cms`, `core-trpc` | §6.5, §6.6 |
| 2 | No React component testing infrastructure | §5, §6.5 |
| 3 | No TDD process documentation (only placement docs exist) | §7.1 |
| 4 | Inline fixtures duplicated across tests; no factories | §5.1, §6.3 |
| 5 | No contract tests — Mock and Payload repos drift independently | §5.2, §6.4 |
| 6 | Vitest base lacks safety defaults (`clearMocks`, `restoreMocks`, jsdom env) | §6.2 |
| 7 | `adding-a-feature.md` does not enforce TDD order | §7.2 |
| 8 | Storybook stories are not executed as tests | §6.8 |
| 9 | Apps have no unit tests (route handlers, providers, bind-production wiring) | §6.7 |
| 10 | No CI — tests can rot silently | §6.11 |

## 4. Architecture overview

Three concentric layers of TDD support:

1. **Tooling layer** — `core-typescript` and `core-eslint` provide configs every package inherits.
2. **Test-utils layer** — a new package `@repo/core-testing` (tag: `tooling`) provides shared helpers: `defineFactory`, `defineContractSuite`, `renderWithProviders`, mock-payload helper, mock-trpc helper, jsdom setup file.
3. **Per-package convention** — every feature/core package follows the same skeleton: factories in `src/__factories__/`, contract suites in `src/__contracts__/`, colocated `*.test.{ts,tsx}` for units, `tests/*.feature.test.ts` for integration.

```
┌─────────────────────────────────────────────────────────────┐
│  apps/* (web-next, web-tanstack, cms, storybook)            │
│  ├─ vitest.config.ts (jsdom)                                 │
│  ├─ src/**/*.test.{ts,tsx}    ← unit + RSC smoke             │
│  └─ e2e/*.spec.ts             ← Playwright (existing)        │
├─────────────────────────────────────────────────────────────┤
│  packages/<feature>/* (auth, blog, media, marketing-pages,   │
│                        navigation)                           │
│  ├─ vitest.config.ts (node by default; jsdom for ui/)        │
│  ├─ src/__factories__/*.factory.ts                           │
│  ├─ src/__contracts__/*-repository.contract.ts               │
│  ├─ src/**/*.test.ts          ← unit                         │
│  └─ tests/*.feature.test.ts   ← feature integration          │
├─────────────────────────────────────────────────────────────┤
│  packages/core-* (shared, ui, api, cms, trpc)                │
│  ├─ vitest.config.ts (jsdom for core-ui; node for rest)      │
│  └─ src/**/*.test.{ts,tsx}    ← composition smoke            │
├─────────────────────────────────────────────────────────────┤
│  packages/core-testing (NEW, tooling tag)                    │
│  ├─ factory/define-factory                                   │
│  ├─ contract/define-contract-suite                           │
│  ├─ react/render-with-providers, mock-trpc                   │
│  ├─ payload/mock-payload-module, stub-config                 │
│  └─ setup/{jsdom,node}                                       │
├─────────────────────────────────────────────────────────────┤
│  packages/core-typescript (tooling)                          │
│  ├─ vitest.base.node.ts   ← safety defaults + coverage       │
│  └─ vitest.base.jsdom.ts  ← extends node + jsdom + setup     │
└─────────────────────────────────────────────────────────────┘
```

Boundary rules unchanged. `core-testing` is `tooling`, so any package may depend on it (devDependency only).

## 5. New package: `@repo/core-testing`

### 5.1 `factory/`

```typescript
// define-factory.ts
export interface FactoryContext {
  sequence: number;
}

export interface Factory<T> {
  build(overrides?: Partial<T>): T;
  buildList(count: number, overrides?: Partial<T>): T[];
  reset(): void;
}

export function defineFactory<T>(builder: (ctx: FactoryContext) => T): Factory<T> {
  let sequence = 0;
  return {
    build(overrides) {
      sequence += 1;
      const base = builder({ sequence });
      return deepMerge(base, overrides ?? {}) as T;
    },
    buildList(count, overrides) {
      return Array.from({ length: count }, () => this.build(overrides));
    },
    reset() {
      sequence = 0;
    },
  };
}
```

Required factories per feature (created in plan):

| Feature | Factories |
|---------|-----------|
| `auth` | `userFactory`, `sessionFactory` |
| `blog` | `articleFactory` |
| `media` | `mediaFactory` |
| `marketing-pages` | `pageFactory`, `siteSettingsFactory` |
| `navigation` | `headerFactory`, `navItemFactory` |

Mock repositories are refactored to consume factories where they need defaults — eliminates per-test inline fixture duplication.

### 5.2 `contract/`

```typescript
// define-contract-suite.ts
export interface ContractContext<T> {
  buildSubject: () => Promise<T> | T;
}

export interface ContractSuite<T> {
  run(buildSubject: () => Promise<T> | T): void;
}

export function defineContractSuite<T>(
  name: string,
  suite: (ctx: ContractContext<T>) => void,
): ContractSuite<T> {
  return {
    run(buildSubject) {
      describe(`Contract: ${name}`, () => {
        suite({ buildSubject });
      });
    },
  };
}
```

Repository interfaces with multiple implementations get a contract suite. The same suite runs against the Mock impl AND the Payload impl (with `vi.mock('payload')`). Required for:

- `IArticlesRepository` (Mock + Payload)
- `IUsersRepository` (Mock + Payload)
- `ISessionsRepository` (Mock + Payload)
- `IMediaRepository` (Mock + Payload)
- `IPagesRepository` (Mock + Payload)
- `ISiteSettingsRepository` (Mock + Payload)
- `IHeaderRepository` (Mock + Payload)

### 5.3 `react/`

```typescript
// render-with-providers.tsx
export interface RenderOptions {
  trpc?: { mocks?: Record<string, unknown> };
  queryClient?: QueryClient;
}

export function renderWithProviders(
  ui: ReactElement,
  options: RenderOptions = {},
): RenderResult & { queryClient: QueryClient } {
  const queryClient = options.queryClient ?? new QueryClient({
    defaultOptions: { queries: { retry: false }, mutations: { retry: false } },
  });
  const trpcClient = createMockTrpcClient(options.trpc?.mocks ?? {});
  const Wrapper = ({ children }: PropsWithChildren) => (
    <QueryClientProvider client={queryClient}>
      <TrpcProvider client={trpcClient} queryClient={queryClient}>
        {children}
      </TrpcProvider>
    </QueryClientProvider>
  );
  return { ...render(ui, { wrapper: Wrapper }), queryClient };
}
```

`createMockTrpcClient` is a thin wrapper that returns hardcoded data per procedure path; full type inference preserved via the `AppRouter` type from `@repo/core-api`.

### 5.4 `payload/`

```typescript
// mock-payload-module.ts
export function mockPayloadModule(impl: Partial<Payload>): void {
  vi.mock('payload', () => ({
    getPayload: vi.fn().mockResolvedValue(impl),
  }));
}

// stub-config.ts
export const stubPayloadConfig = {} as SanitizedConfig;
```

### 5.5 `setup/`

```typescript
// jsdom.ts
import '@testing-library/jest-dom/vitest';
import { afterEach } from 'vitest';
import { cleanup } from '@testing-library/react';

afterEach(() => {
  cleanup();
});

// node.ts
// Currently a no-op; reserved for future global setup.
export {};
```

### 5.6 Package shape

```
packages/core-testing/
├── src/
│   ├── factory/
│   │   ├── define-factory.ts
│   │   ├── define-factory.test.ts
│   │   └── index.ts
│   ├── contract/
│   │   ├── define-contract-suite.ts
│   │   ├── define-contract-suite.test.ts
│   │   └── index.ts
│   ├── react/
│   │   ├── render-with-providers.tsx
│   │   ├── render-with-providers.test.tsx
│   │   ├── mock-trpc.ts
│   │   └── index.ts
│   ├── payload/
│   │   ├── mock-payload-module.ts
│   │   ├── stub-config.ts
│   │   └── index.ts
│   ├── setup/
│   │   ├── jsdom.ts
│   │   └── node.ts
│   └── index.ts
├── package.json     # tag: tooling, exports: ./factory, ./contract, ./react, ./payload, ./setup/jsdom, ./setup/node
├── tsconfig.json
├── vitest.config.ts
└── AGENTS.md
```

`package.json` exports map:

```json
{
  "exports": {
    ".": "./src/index.ts",
    "./factory": "./src/factory/index.ts",
    "./contract": "./src/contract/index.ts",
    "./react": "./src/react/index.ts",
    "./payload": "./src/payload/index.ts",
    "./setup/jsdom": "./src/setup/jsdom.ts",
    "./setup/node": "./src/setup/node.ts"
  }
}
```

## 6. Closing each gap

### 6.1 Tests in core packages (Gap 1)

- **`core-ui`** — jsdom env. Add one `.test.tsx` per primitive (Button, Input, Card, etc. — discovered during execution). Use RTL + `renderWithProviders` (no providers needed for primitives, but pattern uniform).
- **`core-api`** — node env. Test that `appRouter` exposes the expected feature routers (`appRouter._def.procedures` walked recursively).
- **`core-cms`** — node env. Test that the composed Payload config has expected collections + globals (`config.collections.map(c => c.slug)`).
- **`core-trpc`** — node env (provider tests use jsdom). Test that the client factory wires `httpBatchLink` + `superjson`. Use `msw` or fetch stub.

### 6.2 React component testing (Gap 2)

`core-typescript` exports two configs:

```typescript
// vitest.base.node.ts
export const nodeVitestConfig = defineConfig({
  test: {
    globals: true,
    environment: 'node',
    include: ['src/**/*.test.ts', 'tests/**/*.test.ts'],
    setupFiles: ['@repo/core-testing/setup/node'],
    clearMocks: true,
    restoreMocks: true,
    mockReset: true,
    unstubGlobals: true,
    sequence: { shuffle: true },
    coverage: {
      provider: 'v8',
      reporter: ['text', 'html', 'lcov'],
      include: ['src/**'],
      exclude: [
        'src/**/*.test.{ts,tsx}',
        'src/**/index.ts',
        'src/__factories__/**',
        'src/__contracts__/**',
      ],
      thresholds: { statements: 80, branches: 75, functions: 80, lines: 80 },
    },
  },
});

// vitest.base.jsdom.ts
import { mergeConfig } from 'vitest/config';
import { nodeVitestConfig } from './vitest.base.node';

export const jsdomVitestConfig = mergeConfig(nodeVitestConfig, defineConfig({
  test: {
    environment: 'jsdom',
    setupFiles: ['@repo/core-testing/setup/jsdom'],
    include: ['src/**/*.test.{ts,tsx}', 'tests/**/*.test.{ts,tsx}'],
  },
}));
```

### 6.3 Factories (Gap 4)

See §5.1. One factory file per entity, in `src/__factories__/`. Factories deliver stable defaults so snapshot diffs only reflect the SUT's behavior. `__factories__` excluded from coverage.

### 6.4 Contract suites (Gap 5)

See §5.2. One contract suite per repository interface, run against every implementation. Each repo `*.test.ts` becomes ~5 lines: `vi.mock('payload', ...); contractSuite.run(() => new RealRepo(stubConfig));`. Specific edge cases unique to one impl (e.g., Payload doc → domain mapping) stay in the impl-specific test file alongside the contract run.

### 6.5 jsdom + RTL (Gap 2 + Gap 1)

`core-ui` adopts `jsdomVitestConfig`. Test pattern:

```typescript
// packages/core-ui/src/atoms/button/button.test.tsx
import { describe, it, expect } from 'vitest';
import { renderWithProviders } from '@repo/core-testing/react';
import userEvent from '@testing-library/user-event';
import { screen } from '@testing-library/react';
import { Button } from './button';

describe('Button', () => {
  it('renders the label', () => {
    renderWithProviders(<Button>Click me</Button>);
    expect(screen.getByRole('button', { name: 'Click me' })).toBeInTheDocument();
  });

  it('calls onClick when activated', async () => {
    const handleClick = vi.fn();
    renderWithProviders(<Button onClick={handleClick}>Click me</Button>);
    await userEvent.click(screen.getByRole('button'));
    expect(handleClick).toHaveBeenCalledOnce();
  });
});
```

### 6.6 Composition tests for `core-api`, `core-cms`, `core-trpc` (Gap 1)

```typescript
// packages/core-api/src/router.test.ts
describe('appRouter composition', () => {
  it('exposes blog router', () => {
    expect(appRouter._def.procedures).toHaveProperty('blog');
  });
  it('exposes auth, media, marketing-pages, navigation routers', () => { ... });
});

// packages/core-cms/src/config.test.ts
describe('payloadConfig composition', () => {
  it('registers all feature collections', () => {
    const slugs = config.collections.map(c => c.slug);
    expect(slugs).toEqual(expect.arrayContaining(['articles', 'users', 'media', 'pages']));
  });
});
```

### 6.7 App tests (Gap 9)

Per app:

```typescript
// apps/web-next/src/server/bind-production.test.ts
describe('bindProduction', () => {
  it('binds all 4 feature repositories exactly once', async () => {
    const spies = {
      blog: vi.spyOn(blogModule, 'bindProductionArticles'),
      auth: vi.spyOn(authModule, 'bindProductionUsers'),
      media: vi.spyOn(mediaModule, 'bindProductionMedia'),
      marketing: vi.spyOn(marketingModule, 'bindProductionPages'),
    };
    await bindProduction();
    Object.values(spies).forEach(s => expect(s).toHaveBeenCalledOnce());
  });
});

// apps/web-next/src/app/providers.test.tsx
describe('Providers', () => {
  it('wraps children with QueryClientProvider and TrpcProvider', () => {
    renderWithProviders(<Providers><div data-testid="child" /></Providers>);
    expect(screen.getByTestId('child')).toBeInTheDocument();
  });
});

// apps/cms/src/payload.config.test.ts
describe('payload.config', () => {
  it('exports a SanitizedConfig with all feature collections', () => {
    expect(payloadConfig.collections.length).toBeGreaterThanOrEqual(4);
  });
});
```

### 6.8 Storybook test runner (Gap 8)

```bash
pnpm add -D -w @storybook/test-runner playwright --filter @repo/storybook
```

`apps/storybook/package.json` gains:
```json
{
  "scripts": {
    "test-storybook": "test-storybook --url http://localhost:6006"
  }
}
```

Root script: `pnpm test:stories` runs Storybook test-runner against a started Storybook instance. CI builds Storybook static, serves it, runs `test-storybook` against the static URL. Smoke-tests every story (mounts, no console errors).

### 6.9 Coverage thresholds (Gap 6)

Initial threshold: 80% statements / 75% branches / 80% functions / 80% lines (project-wide). `entities/`, `application/use-cases/`, `interface-adapters/controllers/` should hit 100% — enforced via per-directory config:

```typescript
coverage: {
  thresholds: {
    'src/entities/**': { statements: 100, branches: 100 },
    'src/application/use-cases/**': { statements: 100, branches: 95 },
    'src/interface-adapters/controllers/**': { statements: 100, branches: 95 },
    statements: 80, branches: 75, functions: 80, lines: 80,
  },
},
```

Tightening allowed as suite matures. Initial pass may need test additions to cross threshold — included as part of each task.

### 6.10 Sequence shuffling

`sequence: { shuffle: true }` surfaces tests that depend on execution order (a class of flake that's nearly impossible to debug otherwise). If a test fails on a non-default seed, the failure log includes the seed for reproduction.

### 6.11 CI (Gap 10)

`.github/workflows/ci.yml`:

```yaml
name: CI
on:
  push: { branches: [main] }
  pull_request:

env:
  TURBO_TOKEN: ${{ secrets.TURBO_TOKEN }}
  TURBO_TEAM: ${{ vars.TURBO_TEAM }}

jobs:
  validate:
    runs-on: ubuntu-latest
    services:
      postgres:
        image: postgres:16-alpine
        env:
          POSTGRES_PASSWORD: postgres
          POSTGRES_USER: postgres
          POSTGRES_DB: cms
        ports: ['5432:5432']
        options: >-
          --health-cmd "pg_isready -U postgres"
          --health-interval 10s
          --health-timeout 5s
          --health-retries 5
    steps:
      - uses: actions/checkout@v4
      - uses: pnpm/action-setup@v4
        with: { version: 9 }
      - uses: actions/setup-node@v4
        with: { node-version: 22, cache: pnpm }
      - run: pnpm install --frozen-lockfile
      - run: pnpm typecheck
      - run: pnpm lint
      - run: pnpm turbo boundaries
      - run: pnpm test -- --coverage
        env:
          DATABASE_URL: postgres://postgres:postgres@localhost:5432/cms
          PAYLOAD_SECRET: test-secret-do-not-use-in-prod
      - run: pnpm build
      - uses: actions/upload-artifact@v4
        if: always()
        with:
          name: coverage
          path: '**/coverage/lcov.info'

  e2e:
    needs: validate
    runs-on: ubuntu-latest
    services:
      postgres:
        image: postgres:16-alpine
        env: { POSTGRES_PASSWORD: postgres, POSTGRES_USER: postgres, POSTGRES_DB: cms }
        ports: ['5432:5432']
        options: >-
          --health-cmd "pg_isready -U postgres" --health-interval 10s
          --health-timeout 5s --health-retries 5
    steps:
      - uses: actions/checkout@v4
      - uses: pnpm/action-setup@v4
        with: { version: 9 }
      - uses: actions/setup-node@v4
        with: { node-version: 22, cache: pnpm }
      - run: pnpm install --frozen-lockfile
      - run: pnpm exec playwright install --with-deps chromium
      - run: pnpm test:e2e
        env:
          DATABASE_URL: postgres://postgres:postgres@localhost:5432/cms
          PAYLOAD_SECRET: test-secret-do-not-use-in-prod

  storybook:
    needs: validate
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: pnpm/action-setup@v4
        with: { version: 9 }
      - uses: actions/setup-node@v4
        with: { node-version: 22, cache: pnpm }
      - run: pnpm install --frozen-lockfile
      - run: pnpm build-storybook --filter @repo/storybook
      - run: pnpm exec playwright install --with-deps chromium
      - run: pnpm exec concurrently -k -s first -n "SB,TEST" -c "magenta,blue" "pnpm exec http-server apps/storybook/storybook-static --port 6006 --silent" "pnpm exec wait-on tcp:6006 && pnpm test-storybook --filter @repo/storybook"
```

## 7. Documentation changes

### 7.1 New: `docs/guides/tdd-workflow.md`

Outline:
1. **The cycle** — red, green, refactor, with the blog example walked end-to-end.
2. **Test naming** — `describe(SUT)` / `it("does X when Y")`.
3. **AAA structure** — Arrange / Act / Assert with examples.
4. **When to mock — decision tree** (DOT graph):
   ```
   Pure function?       → no mock
   Use case?            → mock repository at DI level (rebind)
   Repository (Payload)?→ mock 'payload' module + use stubPayloadConfig
   Component with data? → renderWithProviders with trpc.mocks
   Route handler?       → mock at boundary only (no deep mocks)
   ```
5. **Test pyramid for this monorepo** — counts per layer; entities + use-cases + controllers > integration > component > e2e.
6. **What NOT to test** — getters/setters, framework code, third-party libs, types-only modules.
7. **Coverage targets** — 80/75/80/80 baseline; 100% in entities + use-cases + controllers.
8. **Factory usage** — when to call `factory.build()` vs construct objects manually.
9. **Contract suite usage** — how to add a new repo impl (write impl, run contract).
10. **Running tests** — watch mode, focused tests (`it.only`), debugging failures.

### 7.2 Restructure: `docs/guides/adding-a-feature.md`

Interleave tests with implementation. Each layer becomes a red-green pair:

```
Step 1: Write failing test for entity schema (Zod parse rejects invalid input)
Step 2: Implement entity to pass
Step 3: Write factory in src/__factories__/<entity>.factory.ts
Step 4: Write failing test for use case using factory + mock repo
Step 5: Implement use case to pass
Step 6: Write contract suite in src/__contracts__/<entity>-repository.contract.ts
Step 7: Implement Mock repo, run contract against it (red → green)
Step 8: Implement Payload repo, run same contract (red → green)
Step 9: Write failing controller test
Step 10: Implement controller to pass
Step 11: Write failing tRPC integration test in tests/<feature>.feature.test.ts
Step 12: Wire router to pass
Step 13: (UI optional) Write failing component test with renderWithProviders
Step 14: Implement component to pass
Step 15: Wire into core-api / core-cms, run typecheck + lint + boundaries
```

Add at top: **"You may not advance to the next layer until the current layer's tests are red, then green."**

### 7.3 Cross-link

`testing-strategy.md` becomes the *placement* doc; `tdd-workflow.md` is the *process* doc. Each links to the other. `AGENTS.md` references both.

### 7.4 ADR

New: `docs/decisions/adr-011-tdd-foundation.md` capturing:
- Why a dedicated `core-testing` package (vs duplicating helpers)
- Why factories instead of fixture files
- Why contract suites instead of separate test files per impl
- Why `sequence.shuffle` (catches order-dependent tests)
- Why `vi.mock('payload')` over a real test DB (speed, determinism)

### 7.5 AGENTS.md updates

Root `AGENTS.md`: add `@repo/core-testing` row to package map, link `docs/guides/tdd-workflow.md`.

Each feature `AGENTS.md`: add a "Tests" section listing factories, contract suites, and example test commands.

Root `CLAUDE.md`: add a "TDD" subsection under Quick Start with the canonical commands.

## 8. Plan structure (preview)

Plan 7 — TDD Foundation, with these tasks (each TDD'd, self-reviewed, two-stage reviewed):

| # | Task | Approx. files |
|---|------|---------------|
| 1 | Scaffold `@repo/core-testing` (TDD itself) | ~20 created |
| 2 | Add jsdom + node Vitest bases to `core-typescript`, migrate 5 feature configs | 2 created, 5 modified |
| 3 | Add factories to all 5 features, refactor mock repos to consume them | 8 created, 5 modified |
| 4 | Define + run contract suites for all 7 repository interfaces | 7 created, 14 modified (each impl `.test.ts` runs the contract) |
| 5 | Add tests + jsdom config to `core-ui` | ~10 created |
| 6 | Add tests + node config to `core-api`, `core-cms`, `core-trpc` | ~10 created |
| 7 | Add unit tests to `apps/web-next`, `apps/web-tanstack`, `apps/cms` | ~10 created |
| 8 | Storybook test-runner integration in `apps/storybook` | 1 modified, 1 created |
| 9 | Write `docs/guides/tdd-workflow.md`, restructure `adding-a-feature.md`, cross-link | 1 created, 2 modified |
| 10 | ADR-011 + AGENTS.md updates + CLAUDE.md update | 1 created, 6 modified |
| 11 | CI workflow `.github/workflows/ci.yml` with services + coverage upload | 1 created |
| 12 | Coverage thresholds enforced; tighten where suites are mature | 0 created, 12 modified (per-package vitest configs) |

Estimated rough total: ~70 files created, ~25 files modified.

## 9. Tradeoffs

| Decision | Pro | Con |
|----------|-----|-----|
| New `core-testing` package | DRY; one canonical place for helpers; testable in isolation | One more package to maintain (but small, mostly stable) |
| Coverage thresholds | Builds fail when coverage drops; agents can't merge regressions | Initial enforcement may need test additions to cross threshold (planned for) |
| Sequence shuffle | Catches order-dependent flakes early | First run may surface latent flakes; we fix them as found |
| `vi.mock('payload')` over real DB in tests | Fast (~ms vs seconds), deterministic, no Docker requirement | Requires contract suite to catch mock/real drift (which is exactly why we add §5.2) |
| Storybook test-runner | Every story becomes a smoke test for free | Adds a CI job (~1-2 min); offset by Turbo cache |
| CI in this template | TDD without CI rots in weeks | Template users must rotate the Turbo token themselves; documented in CI yaml comments |

## 10. Acceptance criteria

- `@repo/core-testing` exists, exports the documented surface, has its own tests passing.
- Every feature has factories in `src/__factories__/` and a contract suite per repository interface.
- `core-ui`, `core-api`, `core-cms`, `core-trpc` each have ≥1 passing test.
- All 4 apps have ≥1 unit test (provider/bind-production/route).
- `pnpm test -- --coverage` passes with thresholds.
- `pnpm test-storybook` passes against built Storybook.
- `docs/guides/tdd-workflow.md` exists; `adding-a-feature.md` interleaves tests with implementation.
- `.github/workflows/ci.yml` runs typecheck, lint, boundaries, test, build, e2e, storybook on every PR.
- ADR-011 committed.
- AGENTS.md and CLAUDE.md reference the new TDD workflow.

## 11. Out of scope (explicit)

- Mutation testing (Stryker)
- Property-based testing (fast-check)
- Visual regression beyond Storybook smoke (Chromatic, Percy)
- Real-DB integration tests (testcontainers Postgres)
- Performance/load testing
- Security scanning in CI (separate concern)

These are good ideas for later but would expand scope past "make TDD frictionless." Tracked as future work.