Add support for RSpec to previews as test cases

[thutterer]

What are you trying to accomplish?

I've noticed that the (Experimental) Previews as test cases don't support RSpec yet, because of how it builds the class name in which it expects the preview:
https://github.com/github/view_component/blob/1a2e39d044f2be8c4dd18fe14d4aa5a3812b79f0/lib/view_component/render_preview_helper.rb#L13-L16

What approach did you choose and why?

This PR adds support for RSpec by checking self.respond_to?(:described_class) and if so, using "#{self.described_class}Preview" as the preview class name.

Anything you want to highlight for special attention from reviewers?

• I haven't added a note about this to the docs. Not sure if that is needed in this case, because if you follow the naming conventions, it will just work.
• I haven't touched any tests. Not sure how RSpec compatibility is handled in the project.
• I haven't added myself to the docs/index.md as I hope Prevent adding existing autoload_paths #1383 gets merged before this one (or eventually).

[joelhawksley]

Wonderful! To little surprise, I'd love to see a test for this ❤️. IMO we should add example rspec tests to the example app. Would you mind doing so in this PR? Just a single test that uses render_preview is sufficient for now, but IMO we should expand what we have for the sake of example.

[thutterer]

IMO we should add example rspec tests to the example app. Would you mind doing so in this PR?

Good idea, I'll do that 👍🏼

[thutterer]

Excuse the 👊🏼 -pushing but I've added the rspec-rails gem and made it so that appraisal rake spec runs all rspec tests.

For now there is only one rspec file covering the fix in this PR. I've added :nocov: comments around the code that is covered with RSpec.

@joelhawksley Should I go ahead and enable this also on CI by running rake test spec instead of rake in the test job?

[joelhawksley]

For now there is only one rspec file covering the fix in this PR. I've added :nocov: comments around the code that is covered with RSpec.

@thutterer yes, let's enable this on CI and remove the :nocov:. Simplecov should collate all of the builds to include the Rspec coverage.

[thutterer]

@joelhawksley

let's enable this on CI and remove the :nocov:. Simplecov should collate all of the builds to include the Rspec coverage.

Done, test coverage back to 100% 💚 I had to move the rspec-rails gem into the top-level Gemfile for rake spec to work without appraisal.

[joelhawksley]

Fantastic! Thanks so much for adding this support ❤️