message: more useful messages from expect().toImplementSystemProps()
diff: @@ -28,16 +28,16 @@ expect.extend({
  toImplementSystemProps(Component, propNames) {
  const missing = propNames.reduce((list, name) => {
  - const prop = systemProps[name]
  + const fn = systemProps[name]
  return list.concat(
  - Object.keys(prop.propTypes).filter(type => {
  + Object.keys(fn.propTypes).filter(type => {
  return !Component.propTypes[type]
  })
  )
  }, [])
  return {
  pass: missing.length === 0,
  - message: () => `Missing props: ${missing.join(', ')}`
  + message: () => `Missing prop${missing.length === 1 ? '' : 's'}: ${missing.join(', ')} (from: ${Object.keys(Component.propTypes).join(', ')})`
  }
  }
  })
  