message: add tests for "is" prop with position components
diff: import React from 'react'
  import {LAYOUT, POSITION} from '../system-props'
  +import Box from '../Box'
  import {Absolute, Fixed, Relative, Sticky} from '../Position'
  import {render} from '../utils/testing'
  @@ -18,6 +19,11 @@ describe('position components', () => {
  it('cannot override position', () => {
  expect(render(<Absolute position="relative" />)).toHaveStyleRule('position', 'absolute')
  })
  + it('can render other components with the is prop', () => {
  + const result = render(<Absolute is={Box} />)
  + expect(result).toHaveStyleRule('position', 'absolute')
  + expect(result).toHaveStyleRule('border', '1px solid')
  + })
  })
  describe('Fixed', () => {
  @@ -30,6 +36,11 @@ describe('position components', () => {
  it('cannot override position', () => {
  expect(render(<Fixed position="relative" />)).toHaveStyleRule('position', 'fixed')
  })
  + it('can render other components with the is prop', () => {
  + const result = render(<Fixed is={Box} />)
  + expect(result).toHaveStyleRule('position', 'fixed')
  + expect(result).toHaveStyleRule('border', '1px solid')
  + })
  })
  describe('Relative', () => {
  @@ -42,6 +53,11 @@ describe('position components', () => {
  it('cannot override position', () => {
  expect(render(<Relative position="absolute" />)).toHaveStyleRule('position', 'relative')
  })
  + it('can render other components with the is prop', () => {
  + const result = render(<Relative is={Box} />)
  + expect(result).toHaveStyleRule('position', 'relative')
  + expect(result).toHaveStyleRule('border', '1px solid')
  + })
  })
  describe('Sticky', () => {
  @@ -54,5 +70,10 @@ describe('position components', () => {
  it('cannot override position', () => {
  expect(render(<Sticky position="absolute" />)).toHaveStyleRule('position', 'sticky')
  })
  + it('can render other components with the is prop', () => {
  + const result = render(<Sticky is={Box} />)
  + expect(result).toHaveStyleRule('position', 'sticky')
  + expect(result).toHaveStyleRule('border', '1px solid')
  + })
  })
  })
  