Functional components with multiple element roots don't mount

[fsblemos]

Version

1.0.0-beta.28

Reproduction link

https://codesandbox.io/s/zkxn8pxpm3?expanddevtools=1&module=%2Fsrc%2Fcomponents%2FHelloWorld.test.js

Steps to reproduce

Create a function component with 2 root elements and try to mount it.

What is expected?

Since functional components can have multiple root elements and works in the browser, mount and shallowMount methods should render it normally too.

What is actually happening?

The component is not mounting and console throws an error (which is not thrown in the browser).

[fsblemos]

An workaround should wrap the component with a root element (like this) then I can test:

it('should support returning more than one root node', () => {
  const wrapper = mount({
    template: `<div><test></test></div>`,
    components: {
      test: {
        functional: true,
        render (h) {
          return [h('span', 'foo'), h('span', 'bar')]
        }
      }
    }
  });
  
  expect(wrapper.html()).toBe('<span>foo</span><span>bar</span>')
})

There is a way vue-test-utils wrap functional components with a root element and return an WrapperArray so we don't need create a root div manually?