old_contents: import py
  
  from ..base import BaseTopazTest
  
  class TestLocalPropagation(BaseTopazTest):
      def test_simple(self, space):
          w_res = space.execute("""
          require "libdeltablue"
  
          string, number = "0", 0
          always predicate: -> { string == number },
                 methods:  -> {[ string <-> { number.to_s },
                                 number <-> { string.to_i } ]}
  
          $res = [string, number]
          string = "23"
          $res << string << number
          number = 7
          $res << string << number
          return $res
          """)
          assert self.unwrap(space, w_res) == ["0", 0, "23", 23, "7", 7]
  
new_contents: import py
  
  from ..base import BaseTopazTest
  
  class TestLocalPropagation(BaseTopazTest):
      def test_simple(self, space):
          w_res = space.execute("""
          require "libdeltablue"
  
          string, number = "0", 0
          always predicate: -> { string == number },
                 methods:  -> {[ string <-> { number.to_s },
                                 number <-> { string.to_i } ]}
  
          $res = [string, number]
          string = "23"
          $res << string << number
          number = 7
          $res << string << number
          return $res
          """)
          assert self.unwrap(space, w_res) == ["0", 0, "23", 23, "7", 7]
  
      def test_class_constraint(self, space):
          w_res = space.execute("""
          require "libdeltablue"
  
          enumerable = nil
          always predicate: -> { enumerable.is_a? Comparable },
                 methods: -> {[ enumerable <-> { "" } ]}
  
          $res = []
          $res << enumerable
          enumerable = 100
          $res << enumerable
          return $res
          """)
          assert self.unwrap(space, w_res) == ["", 100]
  
subject: test for previous commit