See how testing with slots pans out

[boardfish]

Haven't done much testing with slots just here, but I want to make the setup there as easy as possible.

[boardfish]

I guess the ideal thing to aim for here might be:

describe SomeComponent do
  describe "#with_some_slot" do
    let(:component_instance) { component.with_some_slot(...) }
  end
end

And from there, allow folks to choose what they want to vary between each test, whether that's a block for freeform content, args, or both.