Correct implementation of match_prefix es

lib/mutant/context/scope.rb

@@ -96,7 +96,10 @@ module Mutant
       # @api private
       #
       def match_prefixes
-        name_nesting.reverse
+        names = name_nesting
+        names.length.downto(1).map do |last|
+          names[0...last].join('::')
+        end
       end
       memoize :match_prefixes
 

lib/mutant/subject.rb

@@ -99,7 +99,7 @@ module Mutant
     # @api private
     #
     def match_prefixes
-      context.match_prefixes.dup << match_expression
+      [match_expression].concat(context.match_prefixes)
     end
     memoize :match_prefixes