vrandom/tests/pickFromStr.test.js

an easy way to work with random numbers in javascript

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

describe('pickFromStr', () => {
  it('throws an error when called with not a string', () => {
    const str = 123
    expect(() => pickFromStr(str)).toThrowError(TypeError(`${str} is not a string`))
  })

  it('returns an empty string when called with an empty string', () => {
    const str = ''
    const actual = pickFromStr(str)
    const expected = ''
    expect(actual).toBe(expected)
  })

  it.each([
    { string: 'h', mockValue: 0.1, expected: 'h' },
    { string: 'hello', mockValue: 0.1, expected: 'h' },
    { string: 'hello', mockValue: 0.999, expected: 'o' },
    { string: 'hello', mockValue: 0.3, expected: 'e' },
    { string: 'the quick fox jumps over the lazy dog', mockValue: 0.5547, expected: 'o' },
    { string: 'the quick fox jumps over the lazy dog', mockValue: 0.93526, expected: 'd' }
  ])(
    'pickFromStr($str) should return `$expected` when Math.random returns $mockValue',
    ({ string, mockValue, expected }) => {
      jest.spyOn(Math, 'random').mockReturnValueOnce(mockValue)

      const actual = pickFromStr(string)
      expect(actual).toBe(expected)

      Math.random.mockRestore()
    }
  )
})