Simplify method expansions

lib/mutant/constants.rb

@@ -10,10 +10,10 @@ module Mutant
     undef unless until when while yield
   ).map(&:to_sym).to_set.freeze
 
-  METHOD_NAME_EXPANSIONS = {
-    /\?\z/ => '_predicate',
-    /=\z/  => '_writer',
-    /!\z/  => '_bang'
+  METHOD_POSTFIX_EXPANSIONS = {
+    '?' => '_predicate',
+    '=' => '_writer',
+    '!' => '_bang'
   }.freeze
 
   BINARY_METHOD_OPERATOR_EXPANSIONS = {

lib/mutant/strategy/method_expansion.rb

@@ -31,6 +31,8 @@ module Mutant
       end
       private_class_method :map
 
+      REGEXP = /#{Regexp.union(*METHOD_POSTFIX_EXPANSIONS.keys)}\z/.freeze
+
       # Return expanded name
       #
       # @param [Symbol] name
@@ -40,9 +42,7 @@ module Mutant
       # @api private
       #
       def self.expand(name)
-        METHOD_NAME_EXPANSIONS.inject(name.to_s) do |name, find_replace|
-          name.gsub(*find_replace)
-        end.to_sym
+        name.to_s.gsub(REGEXP, METHOD_POSTFIX_EXPANSIONS).to_sym
       end
       private_class_method :expand