How to test that all ActionMailer preview actions render/do not fail?

My app has a lot of mailer actions and previews and I would like to automatically test that all listed mailer preview links respond with HTTP=200/do not fail rendering.

This should solve the problem of duplication between mailer preview actions and specs.

How to do it?

The following solution is not the most optimal(e.g. additional request per each mailer + requires rack_test) but it works:

# cat spec/features/mailer_preview_spec.rb

require 'rails_helper'

RSpec.describe 'MailerPreview', type: :feature do
  before do
    # Assuming you have the Capybara setup
    Capybara.default_driver = :rack_test
  end

  it 'opens /rails/mailers and checks each link' do
    visit '/rails/mailers'
    expect(page.status_code).to eq(200)

    links = page.all('a').map { |link| link[:href] }
    links.each do |link|
      expect {
        visit link
      }.not_to raise_error, "Expected #{link} not to fail"
    end
  end
end

As a reminder, make sure config.action_mailer.show_previews = true is set in test environment for this to work.