test_member.rb: fix locale depending test failure

* test/-ext-/struct/test_member.rb (test_member_get): set
  default_external encoding to fix locale depending test failure.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45466 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/-ext-/struct/test_member.rb

@@ -1,5 +1,6 @@
 require 'test/unit'
 require "-test-/struct"
+require_relative '../../ruby/envutil'
 
 class  Bug::Struct::Test_Member < Test::Unit::TestCase
   S = Bug::Struct.new(:a)
@@ -8,6 +9,8 @@ class  Bug::Struct::Test_Member < Test::Unit::TestCase
     s = S.new(1)
     assert_equal(1, s.get(:a))
     assert_raise_with_message(NameError, /is not a struct member/) {s.get(:b)}
-    assert_raise_with_message(NameError, /\u{3042}/) {s.get(:"\u{3042}")}
+    EnvUtil.with_default_external(Encoding::UTF_8) do
+      assert_raise_with_message(NameError, /\u{3042}/) {s.get(:"\u{3042}")}
+    end
   end
 end