message: update OcticonButton tests
diff: import React from 'react'
  import Octicon from '@githubprimer/octicons-react'
  import OcticonButton from '../OcticonButton'
  -import {render} from '../utils/testing'
  +import {render, rendersClass} from '../utils/testing'
  const Circle = ({r = 8}) => <circle cx={r} cy={r} r={r} />
  Circle.size = [16, 16]
  @@ -41,6 +41,14 @@ describe('OcticonButton', () => {
  expect(render(<OcticonButton icon={Circle} onClick={click} />).props.onClick).toEqual(click)
  })
  + it('respects margin utility prop', () => {
  + expect(rendersClass(<OcticonButton icon={Circle} m={4} />, 'm-4')).toEqual(true)
  + })
  +
  + it('respects padding utility prop', () => {
  + expect(rendersClass(<OcticonButton icon={Circle} p={4} />, 'p-4')).toEqual(true)
  + })
  +
  it('passes the "size" prop to the Octicon', () => {
  expect(render(<OcticonButton icon={Circle} size={128} />)).toEqual(
  render(
  