Added a test that adds a string with a backslash in it

JsonGeneratorTests/JsonArrayTests.cpp

@@ -37,6 +37,13 @@ namespace JsonGeneratorTests
             AssertJsonIs("[\"\\\"\"]");
         }
 
+        TEST_METHOD(AddOneStringContainingBackslash)
+        {
+            arr.add("\\");
+
+            AssertJsonIs("[\"\\\\\"]");
+        }
+
         TEST_METHOD(AddTwoStrings)
         {
             arr.add("hello");