Will this only impact shallowMount? Eg, for components using mount, I think all the prop values should be shown?

It only impact stubbed components so shallowMount and stubs in mount.
I'm also thinking if the props should be sorted by name. I faced some discrepancies of snapshots a while ago because I just changed the order of how the props are passed to the component.

I have added a util function deepCompare and determine the default values of the props during stub setup and not on every render

I'd like some more feedback on this one, maybe @xanf or @cexbrayat or @afontcu ?

My concern is PR adds a lot of complexity that I foresee as difficult to maintain and also will make it very hard to make changes without breaking snapshots.

I'm thinking that VTU should not even be concerned with snapshots; this is a Jest only feature, which can be heavily customized with their snapshot serializer API. Furthermore, different people have different opinions on snapshots, and I don't think we should be enforcing any opinions on them. Knowing the default prop value is likely important for some people.

Finally, this fix is specific to snapshots with shallowMount, a type of test which is going to be brittle and break at the slightest change to any implementation detail (good tests should be resilient to implementation details changing). How useful and beneficial is providing a highly opinionated snapshot, a feature where the desired behavior is different for each dev and testing framework?

I feel like this is going to cause a lot of overhead in the future and we may unintentionally break snapshots in minor versions. I'd like to get some more feedback before we merge this. Thanks for the work so far!

I understand your concerns. Another proposal could be to override the default stub generation by setting a function in the global mounting options. So something like:

const wrapper = shallowMount(MyComponent, {
  global: {
    createStubs: ({ name, component }) => {
      // Implement own logic to create a stub
      return defineComponent({
        name,
        render: () => // Custom render logic
      })
    }
  }
})

This will allow the user the customize the default stub generation when using shallowMount or stubs: { ChildComponent: true }. Maybe some generic function could also be provided by a plugin package

I also tend to think it adds too much complexity for the benefits...

Hi! First of all, thank you for your work on this, I actually learned a couple of things reading your code 🙌

That being said – I agree on the overall feeling of too much complexity – and also, a bit of opinionated. Assuming that component snapshot testing is useful, why wouldn't I get the default values of props? Or why wouldn't I want to break if prop order changes?

With that, I believe this PR should not be merged, as the behavior of snapshot testing is not something Vue Test Utils should control extensively.

Again, thanks!

If you want to make a snapshot serializer that implements this same behavior and need VTU to expose things, we could do that.