Set default_internal and default_external on AS for testing purposes

activesupport/test/abstract_unit.rb

@@ -10,6 +10,14 @@ end
 lib = File.expand_path("#{File.dirname(__FILE__)}/../lib")
 $:.unshift(lib) unless $:.include?('lib') || $:.include?(lib)
 
+require 'active_support/core_ext/string/encoding'
+if "ruby".encoding_aware?
+  # These are the normal settings that will be set up by Railties
+  # TODO: Have these tests support other combinations of these values
+  Encoding.default_internal = "UTF-8"
+  Encoding.default_external = "UTF-8"
+end
+
 require 'test/unit'
 require 'active_support/core_ext/kernel/reporting'
 require 'empty_bool'