Test Factory Patterns

Test Factory Patterns

Overview

Test factories create realistic test data with variety. Good factories generate multiple plausible instances and randomly select one, while allowing partial overrides. Poor factories return identical static data every time.

The Pattern

Good Factory Structure

A well-designed factory:

1. Defines an array of multiple realistic instances with meaningful, varied content
2. Uses randomIn() to select one instance randomly
3. Spreads partial overrides to allow customization

import { Factory, randomIn } from '@packmind/test-utils';
import { Entity, createEntityId } from '@packmind/types';
import { v4 as uuidv4 } from 'uuid';

export const entityFactory: Factory<Entity> = (entity?: Partial<Entity>) => {
  const entities: Entity[] = [
    {
      id: createEntityId(uuidv4()),
      name: 'Meaningful Name One',
      slug: 'meaningful-name-one',
      content: `Realistic content that represents actual usage...`,
      // ... other fields with realistic values
    },
    {
      id: createEntityId(uuidv4()),
      name: 'Different Meaningful Name',
      slug: 'different-meaningful-name',
      content: `Different realistic content...`,
      // ... other fields with different realistic values
    },
    // Add 3-5 varied instances
  ];

  return {
    ...randomIn(entities),
    ...entity,
  };
};

Bad Factory Structure (Avoid)

Avoid factories that return identical static data:

// BAD: Always returns the same data
export const entityFactory: Factory<Entity> = (entity?: Partial<Entity>) => {
  return {
    id: createEntityId(uuidv4()),
    name: 'Test Entity', // Static, meaningless
    content: 'test content', // Not realistic
    ...entity,
  };
};

Guidelines

Content Quality

• Use realistic, domain-appropriate content (not "test", "foo", "bar")
• Include variety that reflects actual usage patterns
• Make names and slugs consistent with each other

Instance Count

• Include 3-5 varied instances in the array
• Each instance should represent a plausible real-world case

Required Imports

import { Factory, randomIn } from '@packmind/test-utils';

ID Generation

• Always generate fresh UUIDs for IDs using createXxxId(uuidv4())
• Never hardcode static UUIDs

Override Support

• Always spread partial overrides last: ...entity
• This allows tests to customize specific fields while keeping realistic defaults