Add rspec world preserve hack

lib/mutant/killer/rspec.rb

@@ -40,6 +40,7 @@ module Mutant
       # @api private
       #
       def run_rspec
+        strategy.prepare_world
         ::RSpec::Core::Runner.run(command_line_arguments, @error_stream, @output_stream)
       end
 

lib/mutant/strategy.rb

@@ -29,6 +29,29 @@ module Mutant
     end
 
     class Rspec < self
+
+      def self.original_world
+        @original_world ||=
+          begin
+            require './spec/spec_helper'
+            ::RSpec.world
+          end
+      end
+
+      def self.prepare_world
+        ::RSpec.instance_variable_set(:@world, original_world)
+        cleanup_world
+      end
+
+      def self.cleanup_world
+        ::RSpec::Core::ExampleGroup.children.clear
+        ::RSpec::Core::ExampleGroup.constants.each do |name|
+          if name =~ /^Nested/
+            RSpec::Core::ExampleGroup.send(:remove_const, name)
+          end
+        end
+      end
+
       KILLER = Killer::Rspec
 
       class DM2 < self