Spec that IO#write does not modify its argument

Author: eregon

spec/ruby/core/io/shared/write.rb

@@ -69,6 +69,16 @@
     lambda { IOSpecs.closed_io.send(@method, "hello") }.should raise_error(IOError)
   end
 
+  it "does not modify the passed argument" do
+    File.open(@filename, "w") do |f|
+      f.set_encoding(Encoding::IBM437)
+      # A character whose codepoint differs between UTF-8 and IBM437
+      f.write "ƒ\n".freeze
+    end
+
+    File.binread(@filename).bytes.should == [159, 10]
+  end
+
   describe "on a pipe" do
     before :each do
       @r, @w = IO.pipe