add test for String#<<

test/test/spec/string_spec.rb

@@ -8,3 +8,22 @@ describe "Strings containing null terminators" do
     s.size.should == 3
   end
 end
+
+describe "String#<< with a codepoint" do
+  it "works on ASCII/BINARY strings" do
+    s = ""
+    s.encoding.should == Encoding::UTF_8
+    s << 3
+    s.should == "\x03"
+
+    s.force_encoding 'ASCII-8BIT'
+    s.encoding.should == Encoding::ASCII_8BIT
+    s << 3
+    s.should == "\x03\x03"
+
+    s.force_encoding 'US-ASCII'
+    s.encoding.should == Encoding::ASCII
+    s << 3
+    s.should == "\x03\x03\x03"
+  end
+end