Fixed defined constants interacting in nested contexts

spec/spec_helper.rb

@@ -31,21 +31,23 @@ module DefinesConstants
   def self.included(example_group)
     example_group.class_eval do
       before do
-        @defined_constants = []
-        @created_tables = []
+        @defined_constants ||= []
+        @created_tables ||= []
       end
 
       after do
         @defined_constants.reverse.each do |path|
           namespace, class_name = *constant_path(path)
           namespace.send(:remove_const, class_name)
         end
+        @defined_constants.clear
 
         @created_tables.each do |table_name|
           ActiveRecord::Base.
             connection.
             execute("DROP TABLE IF EXISTS #{table_name}")
         end
+        @created_tables.clear
       end
 
       def define_class(path, base = Object, &block)