Hi Sanchivan Sivadasan,

You have to create fake response to cover JSON.deserialize.
you can write mock response class and test the same.

here is simple example for your reference:-


public class AnimalLocator {
    
    public class AnimalInstanceClass {
        public Integer id;    
        public String name;    
        public String eats;    
        public String says;    
    } 
    
    public class JSONResponseClass{
        public AnimalInstanceClass animal;
    }
    
    public static String getAnimalNameById (Integer id) {
        Http http = new Http();
        HttpRequest request = new HttpRequest();
        request.setEndpoint('https://th-apex-http-callout.herokuapp.com/animals/' + id);
        request.setMethod('GET');
        HttpResponse response = http.send(request);
        system.debug('response: ' + response.getBody());
        JSONResponseClass results = (JSONResponseClass) JSON.deserialize(response.getBody(), JSONResponseClass.class);
        system.debug('results= ' + results.animal.name);
        return(results.animal.name);
    }

}

Test Class:-

@IsTest
global class AnimalLocatorTest {
    @isTest
    public static void testAnimalLocator() {
        Test.setMock(HttpCalloutMock.class, new AnimalLocatorMock());
        //Httpresponse response = AnimalLocator.getAnimalNameById(1);
        String s =  AnimalLocator.getAnimalNameById(1);
        system.debug('string returned: ' + s);
    }

}

Mock Class:- 

@IsTest
global class AnimalLocatorMock implements HttpCalloutMock {
    
    global HTTPresponse respond(HTTPrequest request) {
        Httpresponse response = new Httpresponse();
        response.setStatusCode(200);
        response.setBody('{"animal":{"id":1,"name":"chicken","eats":"chicken food","says":"cluck cluck"}}');
        return response;
    }

}


Let me know in case of any concerns.

Please mark this answer as the solution/ best answer if it solves your purpose so that it can help other community members.

Thanks,
Pramod Nishane
Salesforce Consultant
Varasi LLC
www.varasi.com