Add test helpers

[PoignardAzur]

AccessKit currently helps you hook into platform APIs, but it doesn't provide an API to maintain and edit a node tree locally for unit tests.

Ideally, my testing workflow would be:

• Create a PersistentNodeTree in my test harness.
• Create a TreeUpdate using my business logic.
• Apply the update to my PersistentNodeTree.
• Query some information about my PersistentNodeTree, and check that it matches my expectations.

"Query some information" could mean getting a Node's value, checking that a given node is in the tree, that a node is another node's child, or just getting a debug representation so I can use insta::assert_debug_snapshot.

Any thoughts?

[DataTriny]

Hello @PoignardAzur,

While its primary focus is not unit testing, how about kittest?

I think our main issue at the moment is that platform adapters each expose slightly different APIs, so providing some sort of testing helper would either mean adding a new adapter that UI toolkits would have to implement, or force testing functionalities into existing adapter. I'm not sure what's the best option.

[PoignardAzur]

I think our main issue at the moment is that platform adapters each expose slightly different APIs,

I don't need to interact with platform adapters. The tests could be purely-platform agnostics: my framework is already producing accessibility nodes, I only need accesskit to store them somewhere.

[mwcampbell]

If you only need a way to store nodes and query them in your tests, you could use accesskit_consumer directly. This is what the third-party kittest project does, apparently using one of our platform adapters as a starting point.

[PoignardAzur]

Alright, I look into that crate.