Add traversal for Fiber test renderer

[sophiebits]

Not clear the path to shipping this but this gives us a migration path internally that we need right now (replaces https://fburl.com/udq9ksvk).

[sophiebits]

@bvaughn Do you want to try to pull this in and see if our tests all pass (or tell me how to do it :p)? I wrote this tonight and the tests (copied from internal https://fburl.com/3vdfoyz7) all pass so it seems too good to be true but maybe.

[bvaughn]

Nice! Yes, I'll run this tomorrow morning.

[bvaughn]

Let's chat when you get in Ben!

[bvaughn]

Looks like CI is failing b'c of Prettier and some Flow issues

[bvaughn]

This looks great Ben!

Aside from the Flow/Prettier issues, LGTM.

By the way, did you intend to add a small test for fragments?

[bvaughn]

nit: The name of this option threw me a bit. To me, "deep" relates to the location within the tree but seems more like returnFirst?

[sophiebits]

Yea it's a little subtle. It's "if a component and its descendants both match, do we return both or just the parent?" You'd think you'd always want all of them but spreading props is common enough that the pattern is painful otherwise unfortunately.

[bvaughn]

That's not how I'm understanding the code. Isn't it a choice between:

• If a component matches, return it, otherwise return the first descendant that matches.
• Return the component and any of its descendants that match.

I think the thing that I find confusing is that deep:false can still return a matching descendant (if the component doesn't match).

Am I misunderstanding this?

[sophiebits]

A
  B {testId: 'foo'}
    div {testId: 'foo'}
  section
    C {testId: 'foo'}
      span {testId: 'foo'}

Finding by props {testId: 'foo'} returns B and C if deep is false but returns B, C, div, and span if deep is true.

Anyway, I didn't write this code – copy/pasted this bit from the internal prototype of this.

[bvaughn]

Ah, I understand. 👍