datetime-commons/src/mediumDateTime.test.ts

import * as fc from 'fast-check'
import mediumDateTime from './mediumDateTime'

// fast-check arbitraries
const isInvalidDate = (d: Date) => isNaN(d.getTime())
const invalidDateString = () => fc.string().filter(s => isInvalidDate(new Date(s)))
const validDateString = () => fc.string().filter(s => !isInvalidDate(new Date(s)))

it('should exist', () => {
  expect(mediumDateTime).toBeDefined()
})

it('should be a callable', () => {
  expect(typeof mediumDateTime).toBe('function')
})

it('should accept a minimum of 1 argument', () => {
  expect(mediumDateTime).toHaveLength(1)
})

describe('on numeric arguments', () => {
  it('should throw an error on NaN', () => {
    expect(() => mediumDateTime(NaN)).toThrow(RangeError)
  })

  it('should return a formatted string', () => {
    fc.assert(
      fc.property(
        fc.integer(),
        v => {
          expect(typeof mediumDateTime(v)).toBe('string')
        }
      )
    )
  })
})

describe('on string arguments', () => {
  it('should throw an error given non-parseable values', () => {
    fc.assert(
      fc.property(
        invalidDateString(),
        v => {
          expect(() => mediumDateTime(v)).toThrow(RangeError)
        }
      )
    )
  })
  it('should return a string given parseable values', () => {
    fc.assert(
      fc.property(
        validDateString(),
        v => {
          expect(typeof mediumDateTime(v)).toBe('string')
        }
      )
    )
  })
})

describe('on object arguments', () => {
  it('should throw an error given non-datelike values', () => {
    fc.assert(
      fc.property(
        fc.object(),
        v => {
          expect(() => mediumDateTime(v)).toThrow(RangeError)
        }
      )
    )
  })

  it('should throw an error given non-datelike arguments', () => {
    fc.assert(
      fc.property(
        fc.anything().filter(v => !['number', 'string', 'object'].includes(typeof v)),
        v => {
          expect(() => mediumDateTime(v)).toThrow(TypeError)
        }
      )
    )
  })

  it('should return a string given date values', () => {
    fc.assert(
      fc.property(
        fc.date(),
        d => {
          expect(typeof mediumDateTime(d)).toBe('string')
        }
      )
    )
  })
})