Add missing escaping of language-tagged literals in Turtle encoder

CHANGELOG.md

@@ -11,6 +11,8 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 
 - the Turtle encoder was encoding IRIs as prefixed names even when they were
   resulting in non-conform prefixed names
+- the Turtle encoder didn't properly escape special characters in language-tagged 
+  literals
 - the `Inspect` protocol implementation for `RDF.Diff` was causing an error when
   both graphs had prefixes defined
   

lib/rdf/serializations/turtle_encoder.ex

@@ -351,7 +351,7 @@ defmodule RDF.Turtle.Encoder do
     do: to_string(bnode)
 
   defp term(%Literal{literal: %LangString{} = lang_string}, _, _, _) do
-    ~s["#{lang_string.value}"@#{lang_string.language}]
+    quoted(lang_string.value) <> "@" <> lang_string.language
   end
 
   defp term(%Literal{literal: %XSD.String{}} = literal, _, _, _) do

test/unit/turtle_encoder_test.exs

@@ -738,6 +738,21 @@ defmodule RDF.Turtle.EncoderTest do
       )
     end
 
+    test "language-tagged literals with newlines embedded are encoded with long quotes" do
+      Turtle.read_string!(~s[<http://a> <http:/b> """testing string parsing in Turtle.
+           """@en .])
+      |> assert_serialization(matches: [~s["""testing string parsing in Turtle.\n]])
+    end
+
+    test "language-tagged literals escaping" do
+      Turtle.read_string!(~s[<http://a> <http:/b> """string with " escaped quote marks"""@en .])
+      |> assert_serialization(
+        matches: [
+          ~r[string with \\" escaped quote mark]
+        ]
+      )
+    end
+
     test "language tagged literals specifies language for literal with language" do
       Turtle.read_string!(~s[<http://a> <http:/b> "string"@en .])
       |> assert_serialization(matches: [~r["string"@en]])