message: fix heading test
diff: /* eslint-disable jsx-a11y/heading-has-content */
  import React from 'react'
  -import {Heading, theme} from '..'
  +import {Heading} from '..'
  import {render, renderStyles} from '../utils/testing'
  +
  +const theme = {
  + breakpoints: ['400px', '640px', '960px', '1280px'],
  + colors: {
  + green: ['#010', '#020', '#030', '#040', '#050', '#060']
  + },
  + fontSizes: [12, 14, 16, 20, 24, 32, 40, 48],
  + fonts: {
  + normal: 'Helvetica,sans-serif',
  + mono: 'Consolas,monospace'
  + },
  + lineHeights: {
  + normal: 1.5,
  + condensed: 1.25,
  + condensedUltra: 1
  + }
  +}
  +
  describe('Heading', () => {
  it('is a system component', () => {
  expect(Heading.systemComponent).toEqual(true)
  