class Shoulda::Matchers::ActiveRecord::HaveAttachedMatcher

def blobs_association_matcher
  @_blobs_association_matcher ||=
    AssociationMatcher.new(
      :"has_#{macro}",
      blobs_association_name,
    ).
      through(attachments_association_name).
      class_name('ActiveStorage::Blob').
      source(:blob)
end