TypeScript Dossier (ts-dossier)

A support library to facilitate the easy creation of test data builders for use with an Object-Mother pattern in TypeScript

Install

npm install @makerx/ts-dossier --save-dev

Usage

The first step is to define a model

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

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

Then define a Builder for that model

import { randomElement, randomNumberBetween, randomString } from '@makerx/ts-dossier'
import { DataBuilder, dossierProxy } from '@makerx/ts-dossier'
import { Shape } from './shape'

function generateSideLengths(sides: number) {
  return [...Array(sides).keys()].map((_) => randomNumberBetween(1, 999))
}

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

  public withSides(sides: number) {
    this.with('sides', sides)
    if (this.thing.sideLengths.length != sides) {
      this.with('sideLengths', generateSideLengths(sides))
    }
    return this
  }

  public asSquare(length: number) {
    this.thing = {
      ...this.thing,
      name: 'Square',
      sides: 4,
      sideLengths: [length, length, length, length],
    }
    return this
  }

  public asIsoscelesTriangle(length: number, perimeter: number) {
    this.thing = {
      ...this.thing,
      name: 'Isosceles triangle',
      sides: 3,
      sideLengths: [length, length, perimeter - length * 2],
    }
    return this
  }
}

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

With the builder defined, and using the dossier proxy, you now have access to the builder methods supplied by the builder itself and the ones defined for you by the Dossier proxy.

Then define a mother to build known models for testing

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

export const shapeMother = {
  blueSquare: () => {
    return shapeBuilder().asSquare(20).withColour('Blue')
  },
  greenTriangle: () => {
    return shapeBuilder().withName('Triangle').withSides(3).withColour('Green')
  },
  redIsoscelesTriangle: () => {
    return shapeBuilder().asIsoscelesTriangle(20, 45).withColour('Red')
  },
}

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.blueSquare().build()
    expect(shape.sides).toBe(4)
  })
  it('has four sides of equal length', () => {
    const shape = shapeMother.blueSquare().build()
    expect(shape.sideLengths).toEqual(expect.arrayContaining([...Array(4)].map((_) => shape.sideLengths[0])))
  })
  it('is named correctly', () => {
    const shape = shapeMother.blueSquare().build()
    expect(shape.name).toBe('Square')
  })
  it('is coloured blue', () => {
    const shape = shapeMother.blueSquare().build()
    expect(shape.colour).toBe('Blue')
  })
})
describe('The isosceles triangle', () => {
  it('has three sides', () => {
    const shape = shapeMother.redIsoscelesTriangle().build()
    expect(shape.sides).toBe(3)
  })
  it('has two sides of equal length', () => {
    const shape = shapeMother.redIsoscelesTriangle().build()
    expect(shape.sideLengths.reduce<number[]>((a, c) => (a.includes(c) ? a : [...a, c]), [])).toHaveLength(2)
  })
  it('is named correctly', () => {
    const shape = shapeMother.redIsoscelesTriangle().build()
    expect(shape.name).toBe('Isosceles triangle')
  })
  it('is coloured red', () => {
    const shape = shapeMother.redIsoscelesTriangle().build()
    expect(shape.colour).toBe('Red')
  })
})

Try it out on StackBlitz

Random Data Builders

Dossier comes with a variety of random data builders - View detailed function descriptions includes arguments in the code docs.

Name	Function	Other
Number	randomNumber
Number between	randomNumberBetween
Float between	randomFloatBetween
String	randomString
ID	randomId
Date	randomDate
Date between	randomDateBetween
Boolean	randomBoolean
Incremented number	incrementedNumber	Returns a unique incremented number. Call resetIncrementedNumbers to reset
Element from a collection	randomElement
Name of a thing	randomThingName
Name of a person	randomPersonName
Email	randomEmail
Phone number	randomPhoneNumber
URL	randomUrl