Easy way to loop over Apex class member variables

Question

So I am writing an API client for some third-party service. I get a response as JSON. now I am getting 100 fields as JSON responses but am consuming only 3 of those columns. I am using strict parsing using JSON.deserialize and deserializing all those 100 fields into apex class member variables for future-proofing it.

Now while writing test classes I need to cover them. Is there Describe Fields equivalent for apex class that I can use to cover those unused columns in test class? It seems quite hectic to just copy-paste 100 lines just to show class variable is being used. I don't wanna use JSON.derializeUntyped as it's not strict parsing which I need. What is the best way to increase coverage for those unused JSON columns for now?

JSON2ApexClass:

public class ResponseWrapper{ 
    @AuraEnabled public Balances balances { get; set; } //Used
    @AuraEnabled public Boolean allowOffset { get; set; }  //Used
    @AuraEnabled public Decimal arrearsTolerancePeriod { get; set; } //Not Used
    @AuraEnabled public Decimal accruedPenalty { get; set; } //NotUsed
   .
   .
//100 such fields

}

Answer 1

There isn't one. There's no standard "reflection" available, so you can't just dynamically access the properties. Either deal with having a huge copy-paste class, or lose the requirement for "strict" validation. It's rarely useful in most practical cases, although that obviously depends on your risk assessment model for unexpected changes.

Answer 2

You can do this trick: create an instance of your class, serialize it and deserialize back to Map. After that you'll have all your fields as keys.

Now it is possible to generate test class (because you have mentioned in the comments, that is it acceptable for you):

ResponseWrapper rw = new ResponseWrapper();
String serializedRw = JSON.serialize(rw);
Map<String, Object> rwMap = (Map<String, Object>) JSON.deserializeUntyped(serializedRw);

String classInstanceName = 'rw';
String className = ResponseWrapper.class.getName();
String testClassBody = '@IsTest\n' 
        + 'private class '+ className + 'Test {\n' 
        + '\t@IsTest\n' 
        + '\tstatic void testMemberVariables(){\n' 
        + '\t\t' + className + ' ' + classInstanceName + ' = new ' + className + '();\n';

for (String memberVariable : rwMap.keySet()) {
    testClassBody += '\t\tSystem.assertEquals(null, ' + classInstanceName + '.' + memberVariable + ');\n';
}

testClassBody += '\t}\n' 
        + '}\n';

System.debug(testClassBody);

HttpRequest req = new HttpRequest();
req.setEndpoint(RestUtils.getSalesforceDomainURL() + '/services/data/v53.0/sobjects/ApexClass');
req.setMethod('POST');
req.setHeader('Content-Type', 'application/json');
req.setHeader('Authorization', 'OAuth ' + UserInfo.getSessionId());
req.setBody(JSON.serialize(new Map<String, String>{
        'Name' => className + 'Test',
        'Body' => testClassBody
}));
Http http = new Http();
HttpResponse res = http.send(req);
res = http.send(req);