Components only returning a render function from setup aren't considered components

[LeBenLeBen]

Subject of the issue

Components using the Composition API that return a render function from setup are not considered valid Vue Components by the internal validator. Consequently, they can’t be used as stubs.

Steps to reproduce

Have a component using the composition API without template and where the render function is returned by the setup function:

import { defineComponent, createElement } from '@vue/composition-api';

export default defineComponent({
  name: 'CFlexItem',

  setup(props, { slots }) {
    return () => {
      return createElement("div", {}, slots.default && slots.default());
    };
  },
});

When trying to mount it like this:

import CFlex from './CFlex';
import CFlexItem from './CFlexItem';

mount(CFlex, {
  stubs: {
    CFlexItem
  },
  slots: {
    default: [
      '<CFlexItem>1</CFlexItem>',
      '<CFlexItem>2</CFlexItem>',
      '<CFlexItem>3</CFlexItem>',
    ],
  },
});

Vue-test-utils throws the following error:

[vue-test-utils]: options.stub values must be passed a string or component

Theses components’ code can be found here.

Expected behaviour

Vue components using solely a render function through setup should be considered valid components.

Possible Solution

Adapt isVueComponent method to handle this specific kind of components. But I’m not sure how this should be done, hints welcome so I can potentially submit a PR.

[lmiller1990]

You could try just adding another condition to isVueComponent. Check if setup exists, and render does not.

I have no idea what will happen - this easiest way to find out would just be going to node_modules/@vue/test-utils/vue-test-utils.js (it is not minified) and adding that in and running your test.