How to test json.deserializeUntyped in trigger

Question

I have a platform event trigger that takes in a json string which contains an array of objects. My postman test call looks like this:

 "testCodeList__c":"[{\"testCode\":\"000000\",\"testName\":\"AAA\",\"procedureClass\":\"XX\"},{\"testCode\":\"111111\",\"testName\":\"BBB\",\"procedureClass\":\"YY\"},{\"testCode\":\"222222\",\"testName\":\"CCC",\"procedureClass\":\"ZZ\"}]"

(note that the quotes are each escaped with backslashes but when I submit this Stack Exchange post, it removes them)

My trigger uses json.deserializeUntyped like this:

List<Object> lstTestCodes = (List<Object>) JSON.deserializeUntyped(evt.testCodeList__c);

This trigger code works just fine, however I cannot get my test class to work. Inside the test class I am setting up a platform event with this parameter:

  testOrder.testCodeList__c = '[{"testCode":"000000","testName":"AAA","procedureClass":"XX"},{"testCode":"111111","testName":"BBB","procedureClass":"YY"},{"testCode":"222222","testName":"CCC","procedureClass":"ZZ"}]';

And when I run the test class, I get 'null input to JSON parser'. I have tried both escaping the quotes with backslash, and not escaping them, but I get the same problem. I have done a ton of Googling. Can anyone show me how I can set up my variable in my Apex test class? thanks!

Answer 1

I would make yourself a small inner class:

public class TestCode {
    public String testCode;
    public String testName;
    public String procedureClass;
}

Use it to both deserialize the incoming json:

TestCode[] codes = (TestCode[])JSON.deserialize(jsonString,TestCode[].class);

And generate the codes you need for your unit test :

new ParentClass.TestCode[] testCodeList = new ParentClass.TestCode[]{
  {'testCode':'000000','testName':'AAA','procedureClass':'XX'},
  {'testCode':'111111','testName':'BBB','procedureClass':'YY'},
  {'testCode':'222222','testName':'CCC','procedureClass':'ZZ'}
};
testOrder.testCodeList__c = JSON.serialize(testCodeList);

I have parent class prefixed above because you'd likely be calling the second code block from the unit test class (I'm assuming)