generate-sample-data

name	generate-sample-data
description	Generate mock/sample data from Zod schemas for testing, development, and mocks. Use when creating sample data generators, setting up test fixtures, populating mock APIs, or generating realistic fake data for development.

Skill: Generate Sample Data from Zod Schemas

Generate type-safe, realistic sample data for testing, development, and mock APIs using Zod schema definitions.

When to Use

• Creating sample data generators for domain models
• Populating MSW mock API handlers
• Generating test fixtures
• Creating Storybook stories
• Seeding development databases
• Building realistic demo data

Technology Stack

Package	Purpose
@anatine/zod-mock	Generates mock data from Zod schemas via generateMock()
@faker-js/faker	Provides realistic fake data
Zod	Source of truth for type definitions and validation

File Structure

model/
├── Job.ts              # Zod schema + type
├── Job.sample.ts       # Sample generator ← THIS FILE
├── User.ts / User.sample.ts
└── index.ts            # Re-export samples

Standard Function Signature

createEntitySample(options?: { seed?: number; overrides?: Partial<Entity> }): Entity

Two Generation Patterns

Pattern 1: Simple Schemas (Primitives Only)

Use generateMock directly:

import { generateMock } from '@anatine/zod-mock';
import { EntitySchema } from './Entity';

export function createEntitySample(options?: { seed?: number; overrides?: Partial<Entity> }): Entity {
  const mock = generateMock(EntitySchema, { seed: options?.seed });
  return { ...mock, ...options?.overrides };
}

Pattern 2: Composed Schemas (Nested Objects/Arrays)

Compose child samples:

export function createJobSample(options?: { seed?: number; overrides?: Partial<Job> }): Job {
  const mock = generateMock(JobBaseSchema, {
    seed: options?.seed,
    stringMap: {
      name: () => faker.company.name(),
      email: () => faker.internet.email(),
    },
  });
  return { ...mock, ...options?.overrides };
}

Enhancing with Faker

Use Faker for realistic names, emails, phones. Create seeded Faker instances for determinism:

import { faker } from '@faker-js/faker';

// Seeded for determinism
if (options?.seed !== undefined) {
  faker.seed(options.seed);
}

Using in Mock APIs (MSW)

Generate 15-20+ items with variety:

const jobs = Array.from({ length: 20 }, (_, i) =>
  createJobSample({ seed: i, overrides: { status: i % 3 === 0 ? 'COMPLETED' : 'ACTIVE' } })
);

Creating Array Samples

export function createJobSamples(count: number, baseSeed: number = 0): Job[] {
  return Array.from({ length: count }, (_, i) =>
    createJobSample({ seed: baseSeed + i })
  );
}

CRITICAL: Deterministic Dates with Seeds

NEVER use Date.now() or new Date() when a seed is provided!

const baseTimestamp = seed !== undefined
  ? new Date(2026, 1, 20, 10, 0, 0).getTime() + (seed * 1000)
  : Date.now();

Testing Sample Generators

Every generator should have tests for:

• Validity (validates against schema)
• Determinism (same seed = same output)
• Overrides work correctly

Key Principles

1. Types derive from Zod schemas
2. JSON serializable only (ISO 8601 strings, not Date objects)
3. Consistent naming: create[Entity]Sample / create[Entity]Samples
4. Seed for determinism
5. Overrides for flexibility
6. Export from model index
7. 15-20+ items for lists/tables

Installation

npm install -D @anatine/zod-mock @faker-js/faker