setProps doesn't update props in some circumstances

[TheCycoONE]

Version

1.0.0-beta.19

Reproduction link

https://codesandbox.io/s/1k6y65wp4

Steps to reproduce

Create a component, like the one in the above reproduction, with multiple properties that are watched.
It is important that the watch function reads one of the properties (i.e. if you remove that switch statement from my test case the problem doesn't happen.)
Create a test for that component, call setProps on the property that is read in the watch.

What is expected?

The property should be updated, the component should react to the updated property

What is actually happening?

The property is never updated. props() shows the old value.

Note: this is a regression, it worked correctly in 1.0.0-beta.16 (I did not try other versions)

[eddyerburgh]

Sorry, this is another problem with how we've implemented synchronous renders.

There's a PR open to fix this by adding an async option to Vue—vuejs/vue#8240.

For the moment, the workaround is to set the sync mounting option to false and use Vue.nextTick/ setTimeout to await DOM updates (like you're doing):

test('use Vue.nextTick', (done) => {
  const wrapper = mount(TestComponent, { sync: false })
  wrapper.trigger('click')
  Vue.nextTick(() => {
    expect(wrapper.text()).toBe('updated')
    done()
  })
})

[TheCycoONE]

Setting sync false and waiting for Vue.nextTick doesn't appear to work around the countingAlgo prop not updating case that started happening after updating from beta 16 to beta 19.

It does workaround the DOM not updating when setProp({value: 42}) is called which was needed in 16 as well.

[HcySunYang]

@TheCycoONE @eddyerburgh
setProps does not work in vue@2.2.6, behaves like this issue, but works fine in the latest version of vue.

[TheCycoONE]

@HcySunYang I am on vue 2.5.16

[agriffis]

@TheCycoONE I'm hitting this too. What are you doing as a workaround?

[TheCycoONE]

Unfortunately I haven't found a workaround yet. For now I'm .skipping those tests.

[agriffis]

I guess npm i -D @vue/test-utils@1.0.0-beta.17 works. 18, 19 and 20 are broken.

[agriffis]

It's hard to pin this bug down. I finally found a minimal failing test: updating a prop that is referenced through a chain of computed and lifecycle hook. I created #820 with that test case.

With that specific configuration, here's the table:

	sync: true	sync: false
1.0.0-beta.17	works	works
1.0.0-beta.18	works	works
1.0.0-beta.19	broken	works
1.0.0-beta.20	broken	works

I think that table changes slightly depending on the exact component configuration, but that's what I found for the minimal test case.