2.0.0-rc.6 Poor error handling with promises & empty wrapper

[Giwayume]

Subject of the issue

If I resolve an empty DOMWrapper as the return value of a promise, which is then awaited by an async function, get this error:

Cannot call then on an empty DOMWrapper.

Steps to reproduce

import { defineComponent, nextTick } from 'vue';
import { mount } from '@vue/test-utils';

async function findAfterNextTick(wrapper, selector) {
    await nextTick();
    return wrapper.find(selector);
}

it('some test', async () => {
    const wrapper = mount(
        defineComponent({
            template: `<div>My component</div>`
        })
    );
    const foundElement = await findAfterNextTick(wrapper, '.something-that-does-not-exist');
    expect(foundElement.exists()).toBeFalsy();
});

Expected behaviour

The test above should pass.

Actual behaviour

Getting this error.

Cannot call then on an empty DOMWrapper.

Possible Solution

This is way too generic.
https://github.com/vuejs/vue-test-utils-next/blob/ecf7905fd36a707174421f5c58b57e000faaf3e0/src/errorWrapper.ts#L11

I'm assuming nodejs is testing if the returned object is thenable, which causes this error. Fix so it's only checking for wrapper properties, just like V1 of @vue/test-utils. Denying all properties is going to lead to weird bugs like this. It may be nice for brevity in your codebase, but it wasn't a smart change.

[lmiller1990]

How about this? #641. I added your test case.

[Giwayume]

That works too, I just worry there's always something you're going to be missing by piecemealing this way.

[lmiller1990]

I'm not sure what "piecemealing" means, but this seems okay. If we run into more problems, we can consider something similar to VTU v1.

[Giwayume]

Piecemeal is to hand-pick, as in add excluded properties as problems are found. I prefer to write code that is safe under unknown conditions, which is the way v1 worked.

[lmiller1990]

Thanks for clarifying that. I see your perspective too; if anything else comes up around this, let's revert to the more boilerplate heavy but reliable style of writing out each method.

I will release this patch soon.