Builder

Test builders are utility classes or functions that simplify the creation of complex test data, primarily focusing on generating entities, commands, and queries. They allow developers to quickly set up and customize test objects with various properties, reducing boilerplate and enhancing test readability. By encapsulating the setup logic, test builders ensure consistency across tests, making it easier to handle varied data scenarios and validate different parts of the application effectively.

Refactoring Guru also write a good article on this topic.

We commonly create builders for 3 different types of classes:

• Commands
• Entities
• Queries

Basic structure

export class EntityBuilder {
  private entity: Entity

  constructor () {
    this.reset()
  }

  reset (): this {
    this.user = new User()

    // ...

    return this
  }

  withProperty (property: string): this {
    this.user.property = property
    
    return this
  }

  build (): User {
    const result = this.user

    this.reset()

    return result
  }
}