Agent skill

generate-factory

Auto-generate test data factories from schemas, types, or models. Use when creating test data infrastructure, setting up fixtures, or reducing test setup boilerplate.

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Install this agent skill to your Project

npx add-skill https://github.com/jmagly/aiwg/tree/main/agentic/code/addons/testing-quality/skills/generate-factory

SKILL.md

Generate Factory Skill

Purpose

Auto-generate test data factories from database schemas, TypeScript interfaces, or model definitions. Factories produce realistic test data using Faker.js patterns, reducing test setup time by 60%.

Research Foundation

Pattern Source Reference
Factory Pattern ThoughtBot FactoryBot
Faker.js Open Source fakerjs.dev
Test Data Management ISTQB CT-TAS Test Automation Strategy
Synthetic Data Tonic.ai Faker Best Practices

When This Skill Applies

  • User needs to create test data factories
  • Setting up test infrastructure for new project
  • Existing tests use hard-coded data
  • Schema/model changes require test data updates
  • Need realistic but deterministic test data

Trigger Phrases

Natural Language Action
"Generate factory for User model" Create user factory
"Create test data factories" Generate factories for all models
"Add faker to tests" Integrate faker with existing tests
"Make test data realistic" Convert hard-coded to factory
"Generate fixtures from schema" Schema-aware factory generation

Factory Concepts

Factory vs Fixture vs Mock

Type Purpose When to Use
Factory Generate dynamic test data When you need many variations
Fixture Static, predefined data When exact values matter
Mock Fake external dependencies When isolating units

Factory Features

typescript
// Basic factory
const user = userFactory.build();
// { id: 'uuid-1', name: 'John Doe', email: 'john@example.com' }

// With overrides
const admin = userFactory.build({ role: 'admin' });
// { id: 'uuid-2', name: 'Jane Doe', email: 'jane@example.com', role: 'admin' }

// Build multiple
const users = userFactory.buildList(5);
// Array of 5 users

// With traits
const inactiveUser = userFactory.build({}, { trait: 'inactive' });
// { id: 'uuid-3', ..., status: 'inactive', deactivatedAt: Date }

// With relationships
const userWithOrders = userFactory.build({}, { with: ['orders'] });
// { id: 'uuid-4', ..., orders: [{ id: 'order-1', ... }] }

Generation Process

1. Analyze Source

Detect schema/type from:

  • TypeScript interfaces
  • Prisma schema
  • JSON Schema
  • Database migrations
  • OpenAPI specs
typescript
// Input: TypeScript interface
interface User {
  id: string;
  name: string;
  email: string;
  age: number;
  role: 'admin' | 'user' | 'guest';
  createdAt: Date;
  preferences?: UserPreferences;
}

2. Map Types to Faker

typescript
const TYPE_MAPPING = {
  // Primitives
  'string': 'faker.string.alphanumeric(10)',
  'number': 'faker.number.int({ min: 0, max: 100 })',
  'boolean': 'faker.datatype.boolean()',
  'Date': 'faker.date.past()',

  // Named fields (semantic mapping)
  'id': 'faker.string.uuid()',
  'name': 'faker.person.fullName()',
  'email': 'faker.internet.email()',
  'phone': 'faker.phone.number()',
  'address': 'faker.location.streetAddress()',
  'age': 'faker.number.int({ min: 18, max: 80 })',
  'createdAt': 'faker.date.past()',
  'updatedAt': 'faker.date.recent()',

  // Enums
  'role': 'faker.helpers.arrayElement(["admin", "user", "guest"])',
};

3. Generate Factory

typescript
// Generated: factories/user.factory.ts
import { faker } from '@faker-js/faker';
import type { User } from '../types';

export const userFactory = {
  /**
   * Build a single User with optional overrides
   */
  build: (overrides: Partial<User> = {}): User => ({
    id: faker.string.uuid(),
    name: faker.person.fullName(),
    email: faker.internet.email(),
    age: faker.number.int({ min: 18, max: 80 }),
    role: faker.helpers.arrayElement(['admin', 'user', 'guest']),
    createdAt: faker.date.past(),
    ...overrides,
  }),

  /**
   * Build multiple Users
   */
  buildList: (count: number, overrides: Partial<User> = {}): User[] =>
    Array.from({ length: count }, () => userFactory.build(overrides)),

  /**
   * Traits for common variations
   */
  traits: {
    admin: { role: 'admin' as const },
    inactive: {
      status: 'inactive',
      deactivatedAt: faker.date.past(),
    },
    newUser: {
      createdAt: faker.date.recent(),
    },
  },

  /**
   * Build with trait
   */
  buildWithTrait: (trait: keyof typeof userFactory.traits, overrides: Partial<User> = {}): User =>
    userFactory.build({ ...userFactory.traits[trait], ...overrides }),
};

4. Generate Related Factories

For entities with relationships:

typescript
// factories/order.factory.ts
import { faker } from '@faker-js/faker';
import { userFactory } from './user.factory';

export const orderFactory = {
  build: (overrides = {}) => ({
    id: faker.string.uuid(),
    userId: faker.string.uuid(),
    items: [],
    total: faker.number.float({ min: 10, max: 500, fractionDigits: 2 }),
    status: faker.helpers.arrayElement(['pending', 'shipped', 'delivered']),
    createdAt: faker.date.past(),
    ...overrides,
  }),

  /**
   * Build with related user
   */
  buildWithUser: (overrides = {}) => {
    const user = userFactory.build();
    return {
      ...orderFactory.build({ userId: user.id, ...overrides }),
      user,
    };
  },
};

Output Format

markdown
## Factory Generation Report

**Source**: `src/types/user.ts`
**Output**: `test/factories/user.factory.ts`

### Generated Factory

```typescript
import { faker } from '@faker-js/faker';
import type { User } from '../../src/types';

export const userFactory = {
  build: (overrides: Partial<User> = {}): User => ({
    id: faker.string.uuid(),
    name: faker.person.fullName(),
    email: faker.internet.email(),
    age: faker.number.int({ min: 18, max: 80 }),
    role: faker.helpers.arrayElement(['admin', 'user', 'guest']),
    createdAt: faker.date.past(),
    preferences: null,
    ...overrides,
  }),

  buildList: (count: number, overrides: Partial<User> = {}): User[] =>
    Array.from({ length: count }, () => userFactory.build(overrides)),

  traits: {
    admin: { role: 'admin' as const },
    inactive: { status: 'inactive' },
  },
};

Field Mappings

Field Type Faker Method
id string faker.string.uuid()
name string faker.person.fullName()
email string faker.internet.email()
age number faker.number.int({ min: 18, max: 80 })
role enum faker.helpers.arrayElement([...])
createdAt Date faker.date.past()

Usage Examples

typescript
// Basic usage
const user = userFactory.build();

// With override
const admin = userFactory.build({ role: 'admin' });

// Multiple users
const users = userFactory.buildList(10);

// With trait
const inactive = userFactory.build(userFactory.traits.inactive);

Dependencies Added

json
{
  "devDependencies": {
    "@faker-js/faker": "^8.0.0"
  }
}


## Deterministic Mode

For tests requiring reproducible data:

```typescript
// Set seed for reproducible data
import { faker } from '@faker-js/faker';

beforeEach(() => {
  faker.seed(12345);  // Same data every run
});

// Or per-factory
export const userFactory = {
  buildDeterministic: (seed: number, overrides = {}) => {
    faker.seed(seed);
    return userFactory.build(overrides);
  },
};

Batch Generation

Generate factories for all models:

bash
# From Prisma schema
npx generate-factory --source prisma/schema.prisma --output test/factories/

# From TypeScript types
npx generate-factory --source src/types/ --output test/factories/

Integration Points

  • Works with tdd-enforce for test data requirements
  • Used by Test Engineer for test creation
  • Feeds into integration test setup
  • Compatible with database seeders

Script Reference

factory_generator.py

Generate factory from schema:

bash
python scripts/factory_generator.py --source src/types/user.ts

batch_generate.py

Generate all factories:

bash
python scripts/batch_generate.py --source src/types/ --output test/factories/

References

  • @$AIWG_ROOT/agentic/code/addons/testing-quality/README.md — Testing quality addon overview
  • @$AIWG_ROOT/agentic/code/frameworks/sdlc-complete/README.md — SDLC framework context for test infrastructure
  • @$AIWG_ROOT/agentic/code/addons/aiwg-utils/rules/research-before-decision.md — Research-first for schema and type analysis
  • @$AIWG_ROOT/docs/cli-reference.md — CLI reference

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