Factorial.test.js

import { factorial } from '../Factorial'

describe('Factorial', () => {
  it('should return factorial 1 for value "0"', () => {
    expect(factorial(0)).toBe(1)
  })

  it('should return factorial 120 for value "5"', () => {
    expect(factorial(5)).toBe(120)
  })

  it('Throw Error for Invalid Input', () => {
    expect(() => factorial('-')).toThrow(
      'Input should be a non-negative whole number'
    )
    expect(() => factorial(null)).toThrow(
      'Input should be a non-negative whole number'
    )
    expect(() => factorial(undefined)).toThrow(
      'Input should be a non-negative whole number'
    )
    expect(() => factorial(3.142)).toThrow(
      'Input should be a non-negative whole number'
    )
    expect(() => factorial(-1)).toThrow(
      'Input should be a non-negative whole number'
    )
  })
})