tailwindcss/tests/negateValue.test.js

import negateValue from '../src/util/negateValue'
import { crosscheck } from './util/run'

crosscheck(() => {
  test('it negates numeric CSS values', () => {
    expect(negateValue('5')).toEqual('-5')
    expect(negateValue('10px')).toEqual('-10px')
    expect(negateValue('18rem')).toEqual('-18rem')
    expect(negateValue('-10')).toEqual('10')
    expect(negateValue('-7ch')).toEqual('7ch')
  })

  test('values that cannot be negated become undefined', () => {
    expect(negateValue('auto')).toBeUndefined()
    expect(negateValue('cover')).toBeUndefined()
  })
})