Use each_value

activesupport/lib/active_support/testing/time_helpers.rb

@@ -23,7 +23,7 @@ def stub_object(object, method_name, return_value)
       end
 
       def unstub_all!
-        @stubs.each do |_, stub|
+        @stubs.each_value do |stub|
           unstub_object(stub)
         end
         @stubs = {}