shoulda.rb

module Shoulda
  module Macros
    def should_change(expression, options = {})
      by, from, to = get_options!([options], :by, :from, :to)
      stmt = "change #{expression.inspect}"
      stmt << " from #{from.inspect}" if from
      stmt << " to #{to.inspect}" if to
      stmt << " by #{by.inspect}" if by

      expression_eval = lambda { eval(expression) }
      before_var_name = '@_before_should_change_' + expression.downcase.gsub(/[^\w]/, '_')
      before = lambda { self.instance_variable_set( before_var_name, expression_eval.bind(self).call ) }
      should stmt, :before => before do
        old_value = self.instance_variable_get( before_var_name )
        new_value = expression_eval.bind(self).call
        assert_operator from, :===, old_value, "#{expression.inspect} did not originally match #{from.inspect}" if from
        assert_not_equal old_value, new_value, "#{expression.inspect} did not change" unless by == 0
        assert_operator to, :===, new_value, "#{expression.inspect} was not changed to match #{to.inspect}" if to
        assert_equal old_value + by, new_value if by
      end
    end

    def should_not_change(expression)
      expression_eval = lambda { eval(expression) }
      before_var_name = '@_before_should_change_' + expression.downcase.gsub(/[^\w]/, '_')
      before = lambda { self.instance_variable_set( before_var_name, expression_eval.bind(self).call ) }
      should "not change #{expression.inspect}", :before => before do
        old_value = self.instance_variable_get( before_var_name )
        new_value = expression_eval.bind(self).call
        assert_equal old_value, new_value, "#{expression.inspect} changed"
      end
    end
  end
end