Oh, module. Modules don't have state, and so can't have attributes without ugly hacks we won't go into.

Given we are in a method with "initialize" in the name, I would suggest a refactor that looks like this, where ParserSupport functionality is rolled into CssParser::Parser.

https://github.com/thoughtbot/shoulda-matchers/blob/master/lib/shoulda/matchers/active_record/association_matcher.rb#L67-L71