Bug: setData with classes/Object prototypes does not work correctly

[jacksongross]

Describe the bug
When testing a component that calls setData with a non-primitive class/object, the object gets set into the component VM without the prototype properties which breaks what should be a straightforward test. If you set the data property on the VM property directly with wrapper.vm.foo = bar it works as expected.

To Reproduce
Made a very basic example that illustrates the bug relating to the mergeDeep behaviour when calling setData
https://stackblitz.com/edit/vue3-script-setup-with-vite-prcxxz?file=src%2Fcomponents%2FHelloWorld.spec.ts,src%2Fcomponents%2FMyObject.js,src%2Fcomponents%2FHelloWorld.vue,src%2FApp.vue

Expected behavior
I expect that calling setData will simply set the property on the component's VM without modification.

Related information:

• @vue/test-utils version: 2.0.0
• Vue version: 3.2.37
• node version: 16.15.0
• npm (or yarn) version: 8.10.0

I can see a fix was applied specifically for Date objects but feel the real problem isn't solved.

[cexbrayat]

Hi @jacksongross

Thanks for the repo! This indeed looks like an issue.

deepMerge probably needs to handle this edge case. Our codebase mentions a SO post that was the source of the algorithm https://stackoverflow.com/questions/27936772/how-to-deep-merge-instead-of-shallow-merge/48218209#48218209

It looks like the answer was updated with a reference to https://jhildenbiddle.github.io/mergician/#/ I wonder if this lib handles this use-case? Maybe we could use it, or at least improve mergeDeep with their findings.

Would you like to try and open a PR to solve it? Any help would be gladly appreciated!

[jacksongross]

Yeah I might take a stab at this when I have some extra time in the next week or so.

[lmiller1990]

Just to check you said

@vue/test-utils version: 2.0.0

We are on 2.2.2 now - there has been many releases since 2.0.0, might be worth updating? That said, I don't think we've changed deepMerge since then.

[jacksongross]

Just to check you said

@vue/test-utils version: 2.0.0

We are on 2.2.2 now - there has been many releases since 2.0.0, might be worth updating? That said, I don't think we've changed deepMerge since then.

It makes no difference -- as you said, the deepMerge hasn't been updated. See https://stackblitz.com/edit/vue3-script-setup-with-vite-prcxxz?file=package.json

[lmiller1990]

Right, fair enough. We should update deepMerge.