1 files changed, 8 insertions, 0 deletions
diff --git a/test/ruby/test_io_buffer.rb b/test/ruby/test_io_buffer.rb
index 385a133421..76fa1bd774 100644
--- a/test/ruby/test_io_buffer.rb
+++ b/test/ruby/test_io_buffer.rb
@@ -83,6 +83,7 @@ class TestIOBuffer < Test::Unit::TestCase
   def test_string_mapped
     string = "Hello World"
     buffer = IO::Buffer.for(string)
+    refute buffer.immutable?
 
     # Cannot modify string as it's locked by the buffer:
     assert_raise RuntimeError do
@@ -99,6 +100,13 @@ class TestIOBuffer < Test::Unit::TestCase
     assert_equal "Hello World", string
   end
 
+  def test_string_mapped_frozen
+    string = "Hello World".freeze
+    buffer = IO::Buffer.for(string)
+
+    assert buffer.immutable?
+  end
+
   def test_non_string
     not_string = Object.new