test refactor, don't hardcode default for `table_name_prefix`.

activerecord/test/cases/ar_schema_test.rb

@@ -34,6 +34,7 @@ def test_schema_define
 
     def test_schema_define_w_table_name_prefix
       table_name = ActiveRecord::SchemaMigration.table_name
+      old_table_name_prefix = ActiveRecord::Base.table_name_prefix
       ActiveRecord::Base.table_name_prefix  = "nep_"
       ActiveRecord::SchemaMigration.table_name = "nep_#{table_name}"
       ActiveRecord::Schema.define(:version => 7) do
@@ -46,7 +47,7 @@ def test_schema_define_w_table_name_prefix
       end
       assert_equal 7, ActiveRecord::Migrator::current_version
     ensure
-      ActiveRecord::Base.table_name_prefix  = ""
+      ActiveRecord::Base.table_name_prefix  = old_table_name_prefix
       ActiveRecord::SchemaMigration.table_name = table_name
     end