This is how I use should_change macros

gistfile1.builder

    context "Parsing example file" do
      setup {
        @xml = File.open(File.expand_path(File.dirname(__FILE__) + '/../EICK.xml'), 'r'){|f| f.read }
        parse_hamweather_data(@xml)
      }
      should_change("the number of forecasts", :by => 8) {Forecast.count}
      should_change("the number of current forecasts", :by => 1) {Forecast.count :conditions => 'current = true'}
      should_change("the number of 3hour forecasts", :by => 7) {Forecast.count :conditions => 'priority = 2'}
    end