test_module.rb: test with UTF-8

* test/ruby/test_module.rb (test_uninitialized_instance_variable):
  test with UTF-8 default external encoding for non-locale
  environments.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48051 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_module.rb

@@ -1829,7 +1829,10 @@ class TestModule < Test::Unit::TestCase
 
     name = "@\u{5909 6570}"
     assert_warning(/instance variable #{name} not initialized/) do
-      assert_nil(a.instance_eval(name))
+      val = EnvUtil.with_default_external(Encoding::UTF_8) {
+        a.instance_eval(name)
+      }
+      assert_nil(val)
     end
   end