test_spec.json

{
  "sample": {
    "valid": ["PK123123","OI2123123","haha"],
    "no_result": ["))kjjkkdf","**kjkljsdf"],
    "bad_format": ["&^&^*^*&*","()()()():P"]
  },
  "test": {
    "basic_test":
    {
      "expect":
      {
        //check against each of result of all trackings
        "exist":[
          "shipment.weight",//single field
          "checkpoints..address.country_iso3"//field in array, use double dot
          ]
      }
    },
    "correctness_test":
    {
      "cases":[
        {
          "description":"it should have sign_by",//optional
          "tracking_numbers":["123123123"],
          "expect":
          {
            "exist":["shipment.signed_by"]
          }
        },
        {
          "description":"it should have no result with invalid number",//optional
          "tracking_numbers":["123123123"],
          "expect":
          {
            "error":801//or Tracking_No_Result(string), check against each tracking in returned result                                                
          }
        },
        {
          "description":"it should have proof or delivery",
          "tracking_numbers":["456456456"],
          "expect":
          {
            "result":[
              //the whole results array
            ]
          }
        },
        {
          "description":"it should have only one tracking error",
          "tracking_numbers":["valid_no","invalid_no"];
          "expect":
          {
            "result":[
              //the whole results array
            ]
          }
        }
      ]
    }    
  }
}

Proposal of flat config

{
    "sample": {
        "valid": ["user1"],
        "no_result": ["))kjjkkdf","**kjkljsdf"],
        "bad_format": ["&^&^*^*&*","()()()():P"]
    },
    "tests": [
        // Basic Test
        {
            //check against each of result of all trackings
            "exist":[
                "shipment.weight",//single field
                "checkpoints..address.country_iso3"//field in array, use double dot
            ]
        },

        // Correctness Test
        {
            "description":"it should have sign_by",//optional
            "tracking_numbers":["123123123"],
            "exist": [
                "shipment.weight",
                {"shipment.signed_by": "John Doe", "shipment.signed_by.OTHER": "..."}
            ]
        }, {
            "description":"it should have no result with invalid number",//optional
            "tracking_numbers":["123123123"],
            "error": 801//or Tracking_No_Result(string), check against each tracking in returned result
        }, {
            "description": "it should have proof or delivery",
            "tracking_numbers": ["456456456"],
            "result": [
                //the whole results array
            ]
        }, {
            "description":"it should have only one tracking error",
            "tracking_numbers":["valid_no","invalid_no"],
            "result": [
                //the whole results array
            ]
        }
    ]
}