A simple set of utility functions to help you perform assertions on JSON output from a JMeter stress test - **no plugins required**

jmeter-json-assertions.js

var testUtil = {
   /**
    * Fails the assertion with the message provided.
    */
   failWith: function (msg) {
      AssertionResult.setFailure(true);
      AssertionResult.setFailureMessage(msg);
   },

   isArray: function (obj) {
      return obj.__proto__.constructor.name === 'Array';
   },

   isObject: function (obj) {
      return obj.__proto__.constructor.name === 'Object';
   },

   /**
    * If the assertion provided is FALSY, the test assertion fails with the message provided
    */
   failIf: function (falseAssertion, msg) {
      if (falseAssertion) {
         this.failWith(msg || JSON.stringify(falseAssertion));
      }
   },

   /**
    * Compares a map of { key: 'Type' } against some target object
    *
    * @param { Object<string, string> } shape For example, { name: 'String', age: 'Number' }
    * @param { Object } target The object to be diffed against the provided shape
    * @return { Object|null } If the output is null, that means the target object has the shape provided, and possibly more attributes
    */
   diffShape: function (shape, target) {
      var mismatch = null;
      Object.keys(shape).some(function (key) {
         if (!target[key]) {
            return mismatch = {
               key: key,
               expected: shape[key],
               actual: String(target[key])
            };
         }

         var targetType = target[key].__proto__.constructor.name;

         if (targetType !== shape[key]) {
            return mismatch = {
               key: key,
               expected: shape[key],
               actual: targetType
            };
         }
      });

      return mismatch;
   }
};


// Example:
var apiResult = {
   users: [
      {
         id: 23,
         name: 'Jack',
         age: 35,
         friends: ['Kate', 'Sawyer']
      },
      {
         id: 42,
         name: 'Jacob',
         age: 1035,
         friends: []
      }
   ]
}

var userShape = {
   id: 'Number',
   name: 'String',
   age: 'Number',
   friends: 'Array'
};


// Usage:

testUtil.isArray(apiResult);
// > false

testUtil.isArray(apiResult.users);
// > true

testUtil.diffShape({users: 'Array'}, apiResult);
// > null
// apiResult has at least a "users" property, which is an Array

testUtil.diffShape({users: 'Array', characters: 'Array'}, apiResult);
// > {key: "characters", expected: "Array", actual: "undefined"}
// apiResult does not have an attribute of "characters", which we expected to be an Array

testUtil.failIf(
   testUtil.diffShape(userShape, apiResult)
);
// > assertion passes, since diffShapes passes FALSY to failIf - which only fails if you send in TRUTH