vrandom/tests/float.test.js

an easy way to work with random numbers in javascript

const float = require('../lib/float.js')

const decimalCount = num => {
  const numStr = num.toString()

  if (numStr.includes('.')) {
    return numStr.split('.')[1].length
  }

  return 0
}

describe('float', () => {
  it('should return a number', () => {
    expect(typeof float(0, 1)).toBe('number')
  })

  it.each([
    { mockValue: 0.5, min: 0, max: 1, decimals: 5, expected: 0.5 },
    { mockValue: 0.45, min: 5, max: 10, decimals: 4, expected: 7.25 },
    { mockValue: 0.912, min: 78, max: 120, decimals: 12, expected: 116.304 },
    { mockValue: 0.004, min: 13, max: 14, decimals: 2, expected: 13 },
    { mockValue: 0.356, min: 32, max: 53, decimals: 1, expected: 39.5 },
    { mockValue: 0.9124, min: 10_005, max: 54_505_502, decimals: 3, expected: 49_731_696.463 },
    { mockValue: 0.671, min: 51, max: 98, decimals: undefined, expected: 82.54 }
  ])(
    'float($min, $max, $decimals) should return $expected when Math.random returns $mockValue',
    ({ mockValue, min, max, decimals, expected }) => {
      jest.spyOn(Math, 'random').mockReturnValueOnce(mockValue)

      const actual = float(min, max, decimals)
      // `toBeCloseTo` matcher is normally appropriate for comparing floats (as it handles floating point imprecision),
      // but we might be alright here to just use `toBe`.
      expect(actual).toBe(expected)

      Math.random.mockRestore()
    }
  )

  it('should return a number between min and max', () => {
    const min = 0
    const max = 1
    for (let i = 0; i < 1000; i++) {
      expect(float(min, max)).toBeGreaterThanOrEqual(min)
      expect(float(min, max)).toBeLessThanOrEqual(max)
    }
  })

  it('should return a number with the specified number of decimals', () => {
    expect(decimalCount(float(0, 1, 0))).toBeLessThanOrEqual(0)
    expect(decimalCount(float(0, 1, 1))).toBeLessThanOrEqual(1)
    expect(decimalCount(float(0, 1, 2))).toBeLessThanOrEqual(2)
    expect(decimalCount(float(0, 1, 3))).toBeLessThanOrEqual(3)
    expect(decimalCount(float(0, 1, 4))).toBeLessThanOrEqual(4)
    expect(decimalCount(float(0, 1, 5))).toBeLessThanOrEqual(5)
    expect(decimalCount(float(0, 1, 6))).toBeLessThanOrEqual(6)
    expect(decimalCount(float(0, 1, 7))).toBeLessThanOrEqual(7)
    expect(decimalCount(float(0, 1, 8))).toBeLessThanOrEqual(8)
    expect(decimalCount(float(0, 1, 9))).toBeLessThanOrEqual(9)
    expect(decimalCount(float(0, 1, 10))).toBeLessThanOrEqual(10)
    expect(decimalCount(float(0, 1, 11))).toBeLessThanOrEqual(11)
    expect(decimalCount(float(0, 1, 12))).toBeLessThanOrEqual(12)
    expect(decimalCount(float(0, 1, 13))).toBeLessThanOrEqual(13)
    expect(decimalCount(float(0, 1, 14))).toBeLessThanOrEqual(14)
    expect(decimalCount(float(0, 1, 15))).toBeLessThanOrEqual(15)
  })

  it('should throw an error if min or max is not a number', () => {
    expect(() => {
      float('a', 1)
    }).toThrowError('min and max must be numbers')

    expect(() => {
      float(1, 'a')
    }).toThrowError('min and max must be numbers')
  })

  it('should throw an error if decimals is not an integer', () => {
    expect(() => {
      float(0, 1, 'a')
    }).toThrowError('decimals must be an integer')
  })

  it('should throw an error if decimals is not between 0 and 15', () => {
    expect(() => {
      float(0, 1, -1)
    }).toThrowError('decimals must be between 0 and 15')

    expect(() => {
      float(0, 1, 16)
    }).toThrowError('decimals must be between 0 and 15')
  })

  it('should throw an error if min is greater than max', () => {
    expect(() => {
      float(1, 0)
    }).toThrowError('first arguments needs to be smaller than second argument')
  })
})