Fix pending spec around string encoding

ext/bson/native.c

@@ -499,17 +499,15 @@ static VALUE rb_string_set_int32(VALUE str, VALUE pos, VALUE an_int32)
  * @example Convert the Ruby string to a BSON string.
  *    rb_string_to_bson_string(0, Qnil, "test");
  *
- * @param [ int ] argc The number or arguments.
- * @param [ Array<Object> ] argv The arguments.
  * @param [ String ] self The string value.
+ * @param [ String ] encoded The encoded string to append to.
  *
  * @return [ String ] The encoded string.
  *
  * @since 2.0.0
  */
-static VALUE rb_string_to_bson_string(int argc, VALUE *argv, VALUE self)
+static VALUE rb_string_to_bson_string(VALUE self, VALUE encoded)
 {
-  VALUE encoded = rb_get_default_encoded(argc, argv);
   VALUE binary = rb_bson_to_utf8_binary(self);
   StringValue(binary);
   rb_str_cat(encoded, RSTRING_PTR(binary), RSTRING_LEN(binary));
@@ -618,8 +616,8 @@ void Init_native()
   // Redefine methods on the String class.
   rb_undef_method(string, "set_int32");
   rb_define_method(string, "set_int32", rb_string_set_int32, 2);
-  rb_undef_method(string, "to_bson_string");
-  rb_define_method(string, "to_bson_string", rb_string_to_bson_string, -1);
+  rb_undef_method(string, "to_utf8_binary");
+  rb_define_private_method(string, "to_utf8_binary", rb_string_to_bson_string, 1);
 
   // Redefine the next method on the object id generator.
   rb_undef_method(generator, "next");

lib/bson/string.rb

@@ -80,7 +80,7 @@ def to_bson_cstring(encoded = ''.force_encoding(BINARY))
     # @since 2.0.0
     def to_bson_string(encoded = ''.force_encoding(BINARY))
       begin
-        encoded << encode(UTF8).force_encoding(BINARY)
+        to_utf8_binary(encoded)
       rescue EncodingError
         data = dup.force_encoding(UTF8)
         raise unless data.valid_encoding?
@@ -129,6 +129,12 @@ def set_int32(pos, int32)
       self[pos, 4] = [ int32 ].pack(Int32::PACK)
     end
 
+    private
+
+    def to_utf8_binary(encoded)
+      encoded << encode(UTF8).force_encoding(BINARY)
+    end
+
     module ClassMethods
 
       # Deserialize a string from BSON.

spec/bson/document_spec.rb

@@ -717,7 +717,7 @@
       end
     end
 
-    pending "when binary strings with utf-8 values exist" do
+    context "when binary strings with utf-8 values exist" do
 
       let(:string) { "europäischen" }
       let(:document) do