How to use helpers in a component and still have previews work?

[unikitty37]

First, let me say that I've read #955, but I can't see how to apply it in this case.

I want to test, in a component test, that a component renders another component; I don't want that test to have to know what that sub-component outputs. I've been reading #1382, and decided to apply a data-test-selector attribute to the component's root, but only in the development and test environments.

I've added this to application_helper.rb:

  def test_selector(value)
    return '' unless Rails.env.development? || Rails.env.test?

    "data-test-selector='#{strip_tags value}'".html_safe
  end

and, in the component's .html.erb file:

<div <%= helpers.test_selector('header-login') %> class="flex flex-col items-end">
  …
</div>

This works perfectly — until I try to preview the component, in which case I get a NoMethodError:

undefined method `test_selector' for #<ActionView::Base:0x00000000032640>

            @output_buffer.safe_append='<div '.freeze;@output_buffer.append=( helpers.test_selector('header-login') );@output_buffer.safe_append=' class="flex flex-col items-end">
                                                                                     ^^^^^^^^^^^^^^

Adding include Rails.application.routes.url_helpers to the component's _preview.rb file doesn't help.

As far as I can see, the solution in #955 involves extensive modifications to each component's class, which doesn't scale for this. Simply adding the attribute to the component rather than using a helper doesn't help, as then it will appear in production. If I was using Webpack or similar, I could have it strip the attribute in the production bundle, but I'm using importmaps.

#1093 looks like it's asking for something similar, but one of the suggested solutions is a hack that will break if sprockets-rails changes its railtie, and another is explicitly disallowing view helpers in previews. If that route's taken, I'll still need a workaround, as I need to use them here.

Is there a simple way to get helpers working in previews without having to perform massive hacks?

[unikitty37]

…and, a few minutes later, inspiration strikes 🙄

Adding the following as lib/view_component_preview.rb solves the problem. Hopefully this monkey-patch doesn't break anything else, but I've not tested it fully yet…

# frozen_string_literal: true

class ViewComponent::Preview
  include Rails.application.routes.url_helpers
end