Improve specs for rb_str_set_len()

Author: eregon

spec/ruby/optional/capi/string_spec.rb

@@ -49,13 +49,24 @@ def to_str
         @s.rb_str_set_len(@str, 8).should == "abcde\x00gh"
       end
 
-      it "updates the byte size and character size" do
+      it "updates the byte size" do
         @s.rb_str_set_len(@str, 4)
         @str.bytesize.should == 4
+        @str.should == "abcd"
+      end
+
+      it "invalidates the character size" do
+        @str.size.should == 10
+        @s.rb_str_set_len(@str, 4)
         @str.size.should == 4
         @str.should == "abcd"
       end
 
+      it "invalidates the code range" do
+        @s.rb_str_set_len(@str, 4)
+        @str.ascii_only?.should == true
+      end
+
       it "updates the string's attributes visible in C code" do
         @s.rb_str_set_len_RSTRING_LEN(@str, 4).should == 4
       end

spec/tags/optional/capi/string_tags.txt

@@ -1 +1,2 @@
 fails:SafeStringValue raises for tained string when $SAFE is 1
+fails:C-API String function rb_str_set_len on a ASCII-8BIT String invalidates the code range