Help with JSON Negative Assertion

Here is the groovy script which extracts the array of "meid" values. Then you can check against array of values.

import groovy.json.JsonSlurper

def str = '''{
  "getCorrectionsResult":{
    "correctionsIdentificationOut":[
      {
        "returnID":1093,
        "meid":673,
        "checkDate":"12/01/2015"
      },
      {
        "returnID":8103,
        "meid":673,
        "checkDate":"02/01/2016"
      }
    ]
  }
}'''

def json = new JsonSlurper().parseText(str)
def existingMeids = json.getCorrectionsResult.correctionsIdentificationOut.meid
def shouldNotBePresent = [671, 672, 980, 994, 993, 995]
//there should not be any common elements between existingMeids and shouldNotBePresent, so intersection is empty
assert [] == existingMeids.intersect(shouldNotBePresent), "There are common meids present which is incorrect"

In the json data, there is 673 present. 

So to make another test if the script is working as desired or not, you can just add 673 to "shouldNotBePresent" list, then the test should fail.