Subquery for json_query is not working, escaping issue with backslashes

Question

I'm executing the following statement:

SELECT 
  json_query (
    (
      SELECT  * FROM 
        (
          SELECT 
            NULL AS test1, 
            NULL AS test2, 
            NULL AS test3, 
            NULL AS test4 
          WHERE 
            1 = 0 
          UNION 
          SELECT 
            CASE WHEN 1 = 0 THEN NULL ELSE 'abc' END AS test1, 
            CASE WHEN 1 = 0 THEN NULL ELSE 'xyz' END AS test2, 
            CASE WHEN 1 = 0 THEN NULL ELSE 'def' END AS test3, 
            json_query (
              CASE WHEN 1 = 0 THEN NULL ELSE (
                SELECT 'abc' AS testsub1 , 
                  ( SELECT '487') AS testsub2 FOR json path, without_array_wrapper
              ) END
            ) AS test4
        ) AS test5 FOR json path
    )
  ) AS [test6] 
ORDER BY 
  1 DESC FOR json path

This is the result:

[
  {
    "test6":[
       {
          "test1":"abc",
          "test2":"xyz",
          "test3":"def",
          "test4":"{\ "testsub1\ ":\ "abc\ ", \" testsub2 \": \ "487 \ "}"
       }
    ]
  }
]

How to avoid the escaping issue in the sub-queries?