test_io.rb: test for rb_io_modestr_fmode

* test/stringio/test_io.rb (test_flag): add assertion for error when
  text and binary mode are mixed.
  [ruby-dev:49465] [Feature #11921]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53379 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 4 insertions, 0 deletions

diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index 2b79acea09..33a2ab883d 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -1906,6 +1906,10 @@ class TestIO < Test::Unit::TestCase
       assert_raise(ArgumentError) do
         open(t.path, "rr") { }
       end
+
+      assert_raise(ArgumentError) do
+        open(t.path, "rbt") { }
+      end
     }
   end