@makerx/ts-object-mother

An ObjectMother support library to facilitate the easy creation of builders in TypeScript

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Install

npm install @makerx/ts-object-mother --save-dev

Usage

The first step is to define a model

type Colour = 'Blue' | 'Red' | 'Yellow' | 'Green'

export type Shape = {
  name: string
  sides: number
  colour: Colour
}

Then define a builder for that model

import { randomElement, randomNumberBetween, randomString } from '@makerx/ts-object-mother'
import { DataBuilder, proxyBuilder } from '@makerx/ts-object-mother'
import { Shape } from './shape'

class ShapeBuilder extends DataBuilder<Shape> {
  constructor() {
    super({
      name: randomString(10, 20),
      sides: randomNumberBetween(1, 4),
      colour: randomElement(['Blue', 'Red', 'Yellow', 'Green']),
    })
  }

  public withName(name: string) {
    return this.with('name', name + ' Intercepted')
  }
}

export const shapeBuilder = proxyBuilder<ShapeBuilder, Shape>(ShapeBuilder)

Then define a mother to build known models for testing

import { shapeBuilder } from './shape-builder'

export const shapeMother = {
  square: () => {
    return shapeBuilder().withName('Square').withSides(4).withColour('Blue')
  },
  triangle: () => {
    return shapeBuilder().withName('Triangle').withSides(3).withColour('Green')
  },
}

And write some tests

import { describe, expect, it } from '@jest/globals'
import { shapeMother } from './shape-mother'

describe('The square', () => {
  it('has four sides', () => {
    const shape = shapeMother.square().build()
    expect(shape.sides).toBe(4)
  })
  it('is named correctly', () => {
    const shape = shapeMother.square().build()
    expect(shape.name).toBe('Square Intercepted')
  })
  it('is coloured blue', () => {
    const shape = shapeMother.square().build()
    expect(shape.colour).toBe('Blue')
  })
})

Try it out on StackBlitz