[minitest] Test view code that use pundit policies

posts_helper.rb

module PostsHelper
  def edit_link
    link_to :Edit, edit_post_path(@post), class: 'btn btn-sm btn-dark' if policy(@post).update?
  end  
end

posts_helper_test.rb

require 'test_helper'

class PostsHelperTest < ActionView::TestCase
  
  test "should return edit link" do
    @post = FactoryBot.create :post
    
    self.current_user = @post.user
    
    assert_dom_equal %{<a class="btn btn-sm btn-dark" href="/posts/#{@post.id}/edit">Edit</a>}, edit_link
  end

end

test_helper.rb

# With the help of the following links, this setup worked for me:
# https://github.com/varvet/pundit/issues/301 (undefined method `policy' for ViewHelper)
# https://www.reddit.com/r/rails/comments/dp70gy/how_to_please_pundit_while_testing_view_helpers/

class ActiveSupport::TestCase
  include Pundit
end

class ActionView::TestCase
  # Used for assigning a user for pundit policies.
  # to assign use `self.current_user` in the test
  def current_user=(user=FactoryBot.create(:user))
    @user = user
  end

  def current_user
    @user
  end
end