Use Mutex from RSpec Support

Author: pirj

lib/rspec/mocks/proxy.rb

@@ -1,3 +1,5 @@
+RSpec::Support.require_rspec_support "mutex"
+
 module RSpec
   module Mocks
     # @private
@@ -9,11 +11,6 @@ def ==(expectation)
         end
       end
 
-      unless defined?(Mutex)
-        Support.require_rspec_support 'mutex'
-        Mutex = Support::Mutex
-      end
-
       # @private
       def ensure_implemented(*_args)
         # noop for basic proxies, see VerifyingProxy for behaviour.
@@ -25,7 +22,7 @@ def initialize(object, order_group, options={})
         @order_group = order_group
         @error_generator = ErrorGenerator.new(object)
         @messages_received = []
-        @messages_received_mutex = Mutex.new
+        @messages_received_mutex = Support::Mutex.new
         @options = options
         @null_object = false
         @method_doubles = Hash.new { |h, k| h[k] = MethodDouble.new(@object, k, self) }