module AssociationSpecs
  class BelongTo
    def initialize(klass)
      @klass = klass
    end

    def matches?(object)
      @object = object
      association_name = @klass.to_s.underscore
      associated_object = @klass.new
      begin
        @object.send("#{association_name}=", associated_object)
        @object.send(association_name) == associated_object
      rescue NoMethodError
        return false
      end
    end

    def failure_message
      "expected #{@object.to_s} to belong to #{@klass.to_s}, but it didn't"
    end

    def negative_failure_message
      "expected #{@object.to_s} not to belong to #{@klass.to_s}, but it did"
    end
  end

  def belong_to(klass)
    BelongTo.new(klass)
  end
end