[react-test-renderer] Fix findByType broken for SimpleMemoComponent

[kevin940726]

Fix #17301 .

The fix is simply check if the tag of the fiber node is SimpleMemoComponent, and check the elementType instead of type.

I'm not fully understand the difference between elementType and type in test-renderer though, looks like if we changed to always get the elementType instead of type would also work? Maybe it has something to do with Lazy and Suspense, but AFAIK react-test-renderer currently doesn't support them.

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[gaearon]

This seems like it would break code searching by the inner type, right? I think we need a more fleshed out proposal for how you imagine this working ideally. You probably don't want different behavior for SimpleMemo and Memo. Overall, I think issues like this show that this whole API is flawed and not something we'd like to keep supporting in longer term. It exposes implementation details.

[bensampaio]

@gaearon what would be a better solution then?

Would it make sense to change the Flow types of React so that you can write findByType(MyComponent.type) without getting type errors? Or would you prefer that findByType accepts memo components as well like proposed in this MR?

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