1 files changed, 11 insertions, 0 deletions
diff --git a/test/stringio/test_stringio.rb b/test/stringio/test_stringio.rb
index c7db91aae1..f4883455f6 100644
--- a/test/stringio/test_stringio.rb
+++ b/test/stringio/test_stringio.rb
@@ -119,6 +119,17 @@ class TestStringIO < Test::Unit::TestCase
     f.close unless f.closed?
   end
 
+  def test_write_infection
+    bug9769 = '[ruby-dev:48118] [Bug #9769]'
+    s = "".untaint
+    f = StringIO.new(s, "w")
+    f.print("bar".taint)
+    f.close
+    assert_predicate(s, :tainted?, bug9769)
+  ensure
+    f.close unless f.closed?
+  end
+
   def test_mode_error
     f = StringIO.new("", "r")
     assert_raise(IOError) { f.write("foo") }