ViewerContext test harness 0.1

[abey79]

What

• Make the render_context field of ViewerContext an Option to make it easier to crate a ViewerContext in a test environment.
• Introduce a (very basic) test helper that creates a ViewerContext for use in unit test.
• Demo unit test that attempts to run SelectionPanel::show_panel()

Chained to #6431

There are many improvements that could be added:

• similar support for ViewportBlueprint
• make re_log::warn/err assert: Add testability features to re_log #6450
• add support for easily populating the stores with data
• benchmarking support?
• etc. etc.

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!

• PR Build Summary
• Recent benchmark results
• Wasm size tracking

To run all checks from main, comment on the PR with @rerun-bot full-check.

[Wumpf]

I wish we could instead have a "null context" on re_renderer, but that would be a lot more work I reckon. Not happy how we have to skip over so much code right now.
That said, approving it regardless since it's a huge improvement of what type of unit tests we can write 👍, TestContext and utility methods that we might add later to it will be invaluable

[Wumpf]

I don't think there's a better way that's not super tricky to implement right now, but this kind of early out here makes this approach a lot less viable for benchmarks. It would be great if we could still some logic of the visualizers, at least including the queries

[abey79]

Agreed. In this case though, literally the next line needs a render_ctx, and it can't be moved further down... 🤷

[Wumpf]

should be protected by cfg test?

[abey79]

It feels like it should, but then cargo clippy --all-features --all-targets fails. I'll leave a todo.